gromacs: Specify c++ stdlib for aocc (#36553)

Co-authored-by: Christoph Junghans <junghans@lanl.gov>

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

@@ -424,6 +424,9 @@ def cmake_args(self):
                 ]
             )
 
+        if self.spec.satisfies("%aocc"):
+            options.append("-DCMAKE_CXX_FLAGS=--stdlib=libc++")
+
         if self.spec.satisfies("@2020:"):
             options.append("-DGMX_INSTALL_LEGACY_API=ON")