Gfortran issues with HSL on Mac

[Sean Anderson]

Perhaps this should be directed to the HSL folks, but I am running into issues with gfortran when trying to install HSL. I'm running Mac OS 10.15.7.

When I run step 6, I get that the Fortran compiler does not work:

```

checking for a BSD-compatible install... /usr/bin/install -c

checking whether build environment is sane... yes

checking for a thread-safe mkdir -p... ./install-sh -c -d

checking for gawk... no

checking for mawk... no

checking for nawk... no

checking for awk... awk

checking whether make sets $(MAKE)... yes

checking whether make supports nested variables... yes

checking for gfortran... gfortran

checking whether the Fortran compiler works... no

configure: error: in `/Users/seananderson/Documents/coinhsl-archive-2021.05.05':

configure: error: Fortran compiler cannot create executables

See `config.log' for more details

```

config.log says `configure: exit 77' at the end

When i run `gfortran -v`, I get:

```

Using built-in specs.

COLLECT_GCC=gfortran

COLLECT_LTO_WRAPPER=/usr/local/Cellar/gcc/10.2.0_4/libexec/gcc/x86_64-apple-darwin19/10.2.0/lto-wrapper

Target: x86_64-apple-darwin19

Configured with: ../configure --build=x86_64-apple-darwin19 --prefix=/usr/local/Cellar/gcc/10.2.0_4 --libdir=/usr/local/Cellar/gcc/10.2.0_4/lib/gcc/10 --disable-nls --enable-checking=release --enable-languages=c,c++,objc,obj-c++,fortran --program-suffix=-10 --with-gmp=/usr/local/opt/gmp --with-mpfr=/usr/local/opt/mpfr --with-mpc=/usr/local/opt/libmpc --with-isl=/usr/local/opt/isl --with-system-zlib --with-pkgversion='Homebrew GCC 10.2.0_4' --with-bugurl=https://github.com/Homebrew/homebrew-core/issues --disable-multilib --with-native-system-header-dir=/usr/include --with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk SED=/usr/bin/sed

Thread model: posix

Supported LTO compression algorithms: zlib

gcc version 10.2.0 (Homebrew GCC 10.2.0_4) 

```

Thanks, and happy to provide any other useful info,

Sean