gcc-7.2.0 fails to build on Ubuntu 18.04: cannot compute suffix of object files

[BJH2017]

Strangely on Ubuntu 18.04 and distributions derived there from (e.g. Mint 19), SageMath fails to build (with the build being performed with the command `make`, if you're wondering), as gcc-7.2.0 fails to compile with the error:

[gcc-7.2.0] make[6]: Leaving directory '/data/GitHub/others/sage/local/var/tmp/sage/build/gcc-7.2.0/gcc-build/gcc'
[gcc-7.2.0] mkdir -p -- x86_64-pc-linux-gnu/libgcc
[gcc-7.2.0] Checking multilib configuration for libgcc...
[gcc-7.2.0] Configuring stage 1 in x86_64-pc-linux-gnu/libgcc
[gcc-7.2.0] configure: creating cache ./config.cache
[gcc-7.2.0] checking build system type... x86_64-pc-linux-gnu
[gcc-7.2.0] checking host system type... x86_64-pc-linux-gnu
[gcc-7.2.0] checking for --enable-version-specific-runtime-libs... no
[gcc-7.2.0] checking for a BSD-compatible install... /usr/bin/install -c
[gcc-7.2.0] checking for gawk... gawk
[gcc-7.2.0] checking for x86_64-pc-linux-gnu-ar... ar
[gcc-7.2.0] checking for x86_64-pc-linux-gnu-lipo... lipo
[gcc-7.2.0] checking for x86_64-pc-linux-gnu-nm... /data/GitHub/others/sage/local/var/tmp/sage/build/gcc-7.2.0/gcc-build/./gcc/nm
[gcc-7.2.0] checking for x86_64-pc-linux-gnu-ranlib... ranlib
[gcc-7.2.0] checking for x86_64-pc-linux-gnu-strip... strip
[gcc-7.2.0] checking whether ln -s works... yes
[gcc-7.2.0] checking for x86_64-pc-linux-gnu-gcc... /data/GitHub/others/sage/local/var/tmp/sage/build/gcc-7.2.0/gcc-build/./gcc/xgcc -B/data/GitHub/others/sage/local/var/tmp/sage/build/gcc-7.2.0/gcc-build/./gcc/ -B/data/GitHub/others/sage/local/x86_64-pc-linux-gnu/bin/ -B/data/GitHub/others/sage/local/x86_64-pc-linux-gnu/lib/ -isystem /data/GitHub/others/sage/local/x86_64-pc-linux-gnu/include -isystem /data/GitHub/others/sage/local/x86_64-pc-linux-gnu/sys-include  
[gcc-7.2.0] checking for suffix of object files... configure: error: in `/data/GitHub/others/sage/local/var/tmp/sage/build/gcc-7.2.0/gcc-build/x86_64-pc-linux-gnu/libgcc':
[gcc-7.2.0] configure: error: cannot compute suffix of object files: cannot compile
[gcc-7.2.0] See `config.log' for more details.
[gcc-7.2.0] Makefile:17525: recipe for target 'configure-stage1-target-libgcc' failed
[gcc-7.2.0] make[5]: *** [configure-stage1-target-libgcc] Error 1

(added a few extra lines for context). This failure occurs with SageMath 8.2 and 8.3beta8. My full log is attached, along with config.log. The output said I should report this here, although I did wonder whether trac.sagemath.org might be the more appropriate place for a bug report like this.

[François Bissey]

Classic error you get when the first pass gcc cannot find the right gmp/mpfr/mpc to load.
It should be visible in the file
/data/GitHub/others/sage/local/var/tmp/sage/build/gcc-7.2.0/gcc-build/x86_64-pc-linux-gnu/libgcc/config.log

François

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> <gcc-7.2.0.log><config.log>

[BJH2017]

Oh, oops should have read it. 'twas merely my own weird environment variables. Should have tried the build in a bash session without a ~/.bashrc file