Failing CI on `macos-latest/gcc-11`

[marcelmbn]

In the CI checks of xtb, the gcc-meson-build (macos-latest, 11) build fails due to errors in compiling the subproject cpx:

 [55/900] Compiling Fortran object subprojects/toml-f/libtoml-f.a.p/src_tomlf_type_array.f90.o
[56/900] Compiling Fortran object subprojects/test-drive/libtest-drive.a.p/src_testdrive.F90.o
[57/900] Compiling Fortran object subprojects/toml-f/libtoml-f.a.p/src_tomlf_type_table.f90.o
[58/900] Module scanner.
[59/900] Compiling C object subprojects/cpx/test/api/cpx_c_test.p/c_api_example.c.o
FAILED: subprojects/cpx/test/api/cpx_c_test.p/c_api_example.c.o 
gcc-11 -Isubprojects/cpx/test/api/cpx_c_test.p -Isubprojects/cpx/test/api -I../subprojects/cpx/test/api -Isubprojects/cpx -I../subprojects/cpx -Isubprojects/numsa/libnumsa.a.p -Isubprojects/mctc-lib/libmctc-lib.a.p -Isubprojects/json-fortran-8.2.5/libjsonfortran.a.p -Isubprojects/toml-f/libtoml-f.a.p -I/opt/homebrew/opt/openblas/include -fdiagnostics-color=always --coverage -std=c11 -O2 -g -fopenmp -MD -MQ subprojects/cpx/test/api/cpx_c_test.p/c_api_example.c.o -MF subprojects/cpx/test/api/cpx_c_test.p/c_api_example.c.o.d -o subprojects/cpx/test/api/cpx_c_test.p/c_api_example.c.o -c ../subprojects/cpx/test/api/c_api_example.c
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/_stdio.h:68,
                 from /opt/homebrew/Cellar/gcc@11/11.4.0/lib/gcc/11/gcc/aarch64-apple-darwin23/11/include-fixed/stdio.h:78,
                 from ../subprojects/cpx/test/api/c_api_example.c:1:
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/cdefs.h:554:30: error: missing ')' after "__has_attribute"
  554 | #if __has_cpp_attribute(clang::unsafe_buffer_usage)
      |                              ^
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/cdefs.h:554:31: error:  ':' without preceding '?'
  554 | #if __has_cpp_attribute(clang::unsafe_buffer_usage)
      |                               ^
[60/900] Compiling Fortran object subprojects/toml-f/libtoml-f.a.p/src_tomlf_type.f90.o
[61/900] Linking static target subprojects/test-drive/libtest-drive.a
[62/900] Compiling Fortran object subprojects/toml-f/libtoml-f.a.p/src_tomlf_diagnostic.f90.o
[63/900] Compiling Fortran object subprojects/json-fortran-8.2.5/libjsonfortran.a.p/src_json_value_module.F90.o
ninja: build stopped: subcommand failed.
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /Users/runner/hostedtoolcache/Python/3.12.4/arm64/bin/ninja -C /Users/runner/work/xtb/xtb/_build
Error: Process completed with exit code 1.