GCC 15 omp.h error when using blis.h from C++

[melven]

GCC 15.1 doesn't like to include omp.h from C++ in an extern "C" region.

However, there is a (unrequired?) #include <omp.h> in blis/blis.h in my installation.

Error message when using blis:

        /scratch/spack-25.2/opt/spack/linux-x86_64_v3/gcc-15.1.0-5n4zqcajsrnaeg7gaijph7rj54fpp76s/bin/g++ -DBLIS_WORKS -isystem /scratch/spack-25.2/opt/spack/linux-x86_64_v3/blis-1.0-nr2wasqmkindwiihhqfsivd7mahspgx7/include/blis -std=gnu
        In file included from ./frame/thread//bli_thrcomm_openmp.h:44,
                         from /home/zoel_ml/tartarus/build/CMakeFiles/CMakeScratch/TryCompile-HUaHcl/src.cxx:1:
        /scratch/spack-25.2/opt/spack/linux-x86_64_v3/gcc-15.1.0-5n4zqcajsrnaeg7gaijph7rj54fpp76s/lib/gcc/x86_64-pc-linux-gnu/15.1.0/include/omp.h:448:1: error: template with C linkage
          448 | template<typename __T, omp_allocator_handle_t __Handle>
              | ^~~~~~~~

Minimal example to demonstrate this behavior in a C++ file:

// works
//#include <omp.h>

// does not work
extern "C" {
#include <omp.h>
}

[devinamatthews]

Hi @melven thanks for reporting this, it should be fixed in #875.

[melven]

Looks good, thanks!