I recently tried a testsuite run with the clang/clang++ compiler. I ran into some failures in gdb.ada due to the use of test_compiler_info. No language argument is specified because ada is not supported, but then the language defaults to c, meaning the compiler info test is done using clang but the compiler used is gnatmake. I disregarded this, because the setup is a bit weird, but today I came across a machine on the gcc compile farm with gnatmake 10.5.0 and gcc 11.4.0, where I run into the exact same problem. A solution could be to drop defaulting to c in test_compiler_info, but it's used in ~300 locations, so that could prove hard to fix manually. Another approach would be to choose the default based on test dir, so ada in gdb.ada and so on. Anyway, probably support for ada needs to be added in test_compiler_info regardless.
I tried to work around this by using CC_FOR_TARGET etc. But we have - gcc-10 and gcc-11 - g++-11 - gfortran-11 - gnatmake-10 so I can't make a set that is consistent.