Using cc -craype-verbose to get cray platform type

lib/spack/spack/platforms/cray_xc.py

@@ -2,6 +2,7 @@
 from spack.architecture import Platform, Target
 from spack.operating_systems.linux_distro import LinuxDistro
 from spack.operating_systems.cnl import Cnl
+from spack.util.executable import which
 
 class CrayXc(Platform):
     priority    = 20
@@ -42,5 +43,11 @@ def __init__(self):
 
     @classmethod
     def detect(self):
-        return os.path.exists('/opt/cray/craype')
+        if os.path.exists('/cray_home'):
+            cc_verbose = which('cc')
+            cc_verbose.add_default_arg('-craype-verbose')
+            text = cc_verbose(output=str, error=str, ignore_errors=True).split()
+            if '-D__CRAYXC' in text:
+                return True
+        return False