Fix pkgconf on Crays (#7171)

This updates Cray.setup_platform_environment to use cray-specific
pkgconfig paths so that all providers of 'pkgconfig' have access
to them (previously the 'pkg-config' provider had this but the
'pkgconf' provider did not).

lib/spack/spack/platforms/cray.py

@@ -108,6 +108,9 @@ def setup_platform_environment(cls, pkg, env):
         if os.path.isdir(cray_wrapper_names):
             env.prepend_path('PATH', cray_wrapper_names)
             env.prepend_path('SPACK_ENV_PATH', cray_wrapper_names)
+        # Makes spack installed pkg-config work on Crays
+        env.append_path("PKG_CONFIG_PATH", "/usr/lib64/pkgconfig")
+        env.append_path("PKG_CONFIG_PATH", "/usr/local/lib64/pkgconfig")
 
     @classmethod
     def detect(cls):