GMP configuration tests fail

Dear experts,

my O2 build fails at GMP@v6.0.0 (on MacOS 10.15.6 (19G2021)).
According to the log it fails during configuration of GMP and can’t find a working compiler (?):

    configure: error: could not find a working compiler, see config.log for details

Looking at the config file it seems like the symbol:


is not available.

Both the log and the config file can be found here:

During the O2 build Clang@llvmorg-10.0.1 was already built succesfully and my system gcc --version yields

Configured with: --prefix=/Applications/ --with-gxx-include-dir=/Applications/
Apple clang version 12.0.0 (clang-1200.0.32.2)
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /Applications/

This problem started to appear after my XCode (Version 12.0 (12A7209)) and most likely also the commandline-tools were updated yesterday.
I already fully removed O2 and reinstalled from scratch but this did not help.

I would appreciate any help.

Thanks in advance,

fixed with latest alidist