Have GROMACS log files indicate spack was used (#25869)

Knowing that spack has patched the code and organized the build is potentially valuable information for GROMACS users and developers troubleshooting their builds.

PLUMED does further patches to GROMACS, so that is expressed directly also.

var/spack/repos/builtin/packages/gromacs/package.py

@@ -390,4 +390,10 @@ def cmake_args(self):
                 options.append('-DFFTWF_LIBRARIES={0}'.
                                format(self.spec['amdfftw'].libs.joined(';')))
 
+        # Ensure that the GROMACS log files report how the code was patched
+        # during the build, so that any problems are easier to diagnose.
+        if '+plumed' in self.spec:
+            options.append('-DGMX_VERSION_STRING_OF_FORK=PLUMED-spack')
+        else:
+            options.append('-DGMX_VERSION_STRING_OF_FORK=spack')
         return options