warpx: Fixes for building on NERSC (#9671)

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

@@ -74,5 +74,11 @@ def torf(s):
                         'TINY_PROFILE = {0}'.format(torf('+tprof')))
         makefile.filter('EBASE .*', 'EBASE = warpx')
 
+    def setup_environment(self, spack_env, run_env):
+        # --- Fool the compiler into using the "unknown" configuration.
+        # --- With this, it will use the spack provided mpi.
+        spack_env.set('HOSTNAME', 'unknown')
+        spack_env.set('NERSC_HOST', 'unknown')
+
     def install(self, spec, prefix):
         make('WarpxBinDir = {0}'.format(prefix.bin), 'all')