I went back and reread the posts here and ultimately discovered the brew llvm wasn't installed on my system. I was using the one that came with Xcode 10.1. When I tried to install brew's llvm, it failed, as did brew's gcc 11.
╰──► % brew install llvm
Running `brew update --auto-update`...
==> Auto-updated Homebrew!
Updated 2 taps (homebrew/core and homebrew/cask).
==> Modified Formulae
Modified 11 formulae.
==> Modified Casks
Modified 1 cask.
Warning: You are using macOS 10.13.
We (and Apple) do not provide support for this old version.
You will encounter build failures with some formulae.
Please create pull requests instead of asking for help on Homebrew's GitHub,
Twitter or any other official channels. You are responsible for resolving
any issues you experience while you are running this
old version.
==> Downloading https://github.com/llvm/llvm-project/releases/download/llvmorg-14.0.6/llvm-project-14.0.6.src.tar.xz
Already downloaded: /Users/vilain/Library/Caches/Homebrew/downloads/ca2953276467b5dcc28485aa2b1afc3bcf32bbf84d5e0236f6284234afca2d8d--llvm-project-14.0.6.src.tar.xz
==> cmake -G Unix Makefiles .. -DLLVM_ENABLE_PROJECTS=clang;clang-tools-extra;lld;lldb;mlir;polly -DLLVM_ENABLE_RUNTIMES=compiler-rt;libcxx;libc
==> cmake --build .
Last 15 lines from /Users/vilain/Library/Logs/Homebrew/llvm/02.cmake:
[ 81%] Linking CXX static library ../../../../../../lib/liblldbPluginPlatformQemuUser.a
cd /tmp/llvm-20220713-79362-b0pdl1/llvm-project-14.0.6.src/llvm/build/tools/lldb/source/Plugins/Platform/QemuUser && /usr/local/Cellar/cmake/3.23.2/bin/cmake -P CMakeFiles/lldbPluginPlatformQemuUser.dir/cmake_clean_target.cmake
cd /tmp/llvm-20220713-79362-b0pdl1/llvm-project-14.0.6.src/llvm/build/tools/lldb/source/Plugins/Platform/QemuUser && /usr/local/Cellar/cmake/3.23.2/bin/cmake -E cmake_link_script CMakeFiles/lldbPluginPlatformQemuUser.dir/link.txt --verbose=1
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool" -static -no_warning_for_no_symbols -o ../../../../../../lib/liblldbPluginPlatformQemuUser.a CMakeFiles/lldbPluginPlatformQemuUser.dir/PlatformQemuUser.cpp.o
[ 81%] Built target lldbPluginPlatformQemuUser
[ 81%] Linking CXX static library ../../../lib/liblldELF.a
cd /tmp/llvm-20220713-79362-b0pdl1/llvm-project-14.0.6.src/llvm/build/tools/lld/ELF && /usr/local/Cellar/cmake/3.23.2/bin/cmake -P CMakeFiles/lldELF.dir/cmake_clean_target.cmake
cd /tmp/llvm-20220713-79362-b0pdl1/llvm-project-14.0.6.src/llvm/build/tools/lld/ELF && /usr/local/Cellar/cmake/3.23.2/bin/cmake -E cmake_link_script CMakeFiles/lldELF.dir/link.txt --verbose=1
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool" -static -no_warning_for_no_symbols -o ../../../lib/liblldELF.a CMakeFiles/lldELF.dir/AArch64ErrataFix.cpp.o CMakeFiles/lldELF.dir/Arch/AArch64.cpp.o CMakeFiles/lldELF.dir/Arch/AMDGPU.cpp.o CMakeFiles/lldELF.dir/Arch/ARM.cpp.o CMakeFiles/lldELF.dir/Arch/AVR.cpp.o CMakeFiles/lldELF.dir/Arch/Hexagon.cpp.o CMakeFiles/lldELF.dir/Arch/Mips.cpp.o CMakeFiles/lldELF.dir/Arch/MipsArchTree.cpp.o CMakeFiles/lldELF.dir/Arch/MSP430.cpp.o CMakeFiles/lldELF.dir/Arch/PPC.cpp.o CMakeFiles/lldELF.dir/Arch/PPC64.cpp.o CMakeFiles/lldELF.dir/Arch/RISCV.cpp.o CMakeFiles/lldELF.dir/Arch/SPARCV9.cpp.o CMakeFiles/lldELF.dir/Arch/X86.cpp.o CMakeFiles/lldELF.dir/Arch/X86_64.cpp.o CMakeFiles/lldELF.dir/ARMErrataFix.cpp.o CMakeFiles/lldELF.dir/CallGraphSort.cpp.o CMakeFiles/lldELF.dir/DWARF.cpp.o CMakeFiles/lldELF.dir/Driver.cpp.o CMakeFiles/lldELF.dir/DriverUtils.cpp.o CMakeFiles/lldELF.dir/EhFrame.cpp.o CMakeFiles/lldELF.dir/ICF.cpp.o CMakeFiles/lldELF.dir/InputFiles.cpp.o CMakeFiles/lldELF.dir/InputSection.cpp.o CMakeFiles/lldELF.dir/LTO.cpp.o CMakeFiles/lldELF.dir/LinkerScript.cpp.o CMakeFiles/lldELF.dir/MapFile.cpp.o CMakeFiles/lldELF.dir/MarkLive.cpp.o CMakeFiles/lldELF.dir/OutputSections.cpp.o CMakeFiles/lldELF.dir/Relocations.cpp.o CMakeFiles/lldELF.dir/ScriptLexer.cpp.o CMakeFiles/lldELF.dir/ScriptParser.cpp.o CMakeFiles/lldELF.dir/SymbolTable.cpp.o CMakeFiles/lldELF.dir/Symbols.cpp.o CMakeFiles/lldELF.dir/SyntheticSections.cpp.o CMakeFiles/lldELF.dir/Target.cpp.o CMakeFiles/lldELF.dir/Thunks.cpp.o CMakeFiles/lldELF.dir/Writer.cpp.o
[ 81%] Built target lldELF
[ 81%] Linking CXX shared library ../../../../lib/libclang.dylib
cd /tmp/llvm-20220713-79362-b0pdl1/llvm-project-14.0.6.src/llvm/build/tools/clang/tools/libclang && /usr/local/Cellar/cmake/3.23.2/bin/cmake -E cmake_link_script CMakeFiles/libclang.dir/link.txt --verbose=1
/usr/local/Homebrew/Library/Homebrew/shims/mac/super/clang++ -march=core2 -stdlib=libc++ -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fno-common -Woverloaded-virtual -Wno-nested-anon-types -O3 -DNDEBUG -dynamiclib -Wl,-headerpad_max_install_names -Wl,-dead_strip -Wl,-exported_symbols_list,"/tmp/llvm-20220713-79362-b0pdl1/llvm-project-14.0.6.src/llvm/build/tools/clang/tools/libclang/libclang.exports" -Wl,-compatibility_version -Wl,1 -Wl,-current_version -Wl,14.0.6 -stdlib=libc++ -o ../../../../lib/libclang.dylib -install_name @rpath/libclang.dylib CMakeFiles/libclang.dir/ARCMigrate.cpp.o CMakeFiles/libclang.dir/BuildSystem.cpp.o CMakeFiles/libclang.dir/CIndex.cpp.o CMakeFiles/libclang.dir/CIndexCXX.cpp.o CMakeFiles/libclang.dir/CIndexCodeCompletion.cpp.o CMakeFiles/libclang.dir/CIndexDiagnostic.cpp.o CMakeFiles/libclang.dir/CIndexHigh.cpp.o CMakeFiles/libclang.dir/CIndexInclusionStack.cpp.o CMakeFiles/libclang.dir/CIndexUSRs.cpp.o CMakeFiles/libclang.dir/CIndexer.cpp.o CMakeFiles/libclang.dir/CXComment.cpp.o CMakeFiles/libclang.dir/CXCursor.cpp.o CMakeFiles/libclang.dir/CXIndexDataConsumer.cpp.o CMakeFiles/libclang.dir/CXCompilationDatabase.cpp.o CMakeFiles/libclang.dir/CXLoadedDiagnostic.cpp.o CMakeFiles/libclang.dir/CXSourceLocation.cpp.o CMakeFiles/libclang.dir/CXStoredDiagnostic.cpp.o CMakeFiles/libclang.dir/CXString.cpp.o CMakeFiles/libclang.dir/CXType.cpp.o CMakeFiles/libclang.dir/Indexing.cpp.o CMakeFiles/libclang.dir/FatalErrorHandler.cpp.o CMakeFiles/libclang.dir/Rewrite.cpp.o -Wl,-rpath,@loader_path/../lib ../../../../lib/libclangAST.a ../../../../lib/libclangBasic.a ../../../../lib/libclangDriver.a ../../../../lib/libclangFrontend.a ../../../../lib/libclangIndex.a ../../../../lib/libclangLex.a ../../../../lib/libclangRewrite.a ../../../../lib/libclangSema.a ../../../../lib/libclangSerialization.a ../../../../lib/libclangTooling.a ../../../../lib/libclangARCMigrate.a ../../../../lib/libclangFormat.a ../../../../lib/libclangToolingInclusions.a ../../../../lib/libclangToolingCore.a ../../../../lib/libclangFrontend.a ../../../../lib/libclangDriver.a ../../../../lib/libclangParse.a ../../../../lib/libclangRewrite.a ../../../../lib/libclangSerialization.a ../../../../lib/libclangSema.a ../../../../lib/libclangEdit.a ../../../../lib/libclangAnalysis.a ../../../../lib/libclangASTMatchers.a ../../../../lib/libclangAST.a ../../../../lib/libclangLex.a ../../../../lib/libclangBasic.a ../../../../lib/libLLVM.dylib
[ 81%] Built target libclang
gmake: *** [all] Error 2
Do not report this issue to Homebrew/brew or Homebrew/core!
isl is a requirement for btop and gcc. Otherwise, I don't need it on my machine. Given the unsupported nature of brew on 10.13 and the parts required to maintain btop (it took 3 hours to compile), I stripped it along with gcc and isl from my system.
So there's no log to see.
Thanks for your help, though.