python: RPATH on Cray (#4209)

* python: ensure that distutils sets valid compiler options for RPATH on cray

* python: add cray-rpath patches for python@2.3:3.0.1 and python@3.1:

* python: in patch(..., when="@a:b platform=c"), limit b must be specified

* python: assume that python@4 will break the cray patches

var/spack/repos/builtin/packages/python/cray-rpath-2.3.patch

@@ -0,0 +1,12 @@
+--- a/Lib/distutils/unixccompiler.py	2003-06-02 05:27:40.000000000 +1000
++++ b/Lib/distutils/unixccompiler.py	2017-05-13 13:52:45.554213616 +1000
+@@ -208,7 +208,8 @@
+         elif compiler[:3] == "gcc" or compiler[:3] == "g++":
+           return "-Wl,-R" + dir
+         else:
+-            return "-R" + dir
++            # Patched by spack to use gcc syntax by default:
++            return "-Wl,-R" + dir
+ 
+     def library_option(self, lib):
+         return "-l" + lib

var/spack/repos/builtin/packages/python/cray-rpath-3.1.patch

@@ -0,0 +1,15 @@
+--- a/Lib/distutils/unixccompiler.py	2009-05-09 21:55:12.000000000 +1000
++++ b/Lib/distutils/unixccompiler.py	2017-05-13 14:30:18.077518999 +1000
+@@ -299,10 +299,8 @@
+                 else:
+                     return "-Wl,-R" + dir
+             else:
+-                # No idea how --enable-new-dtags would be passed on to
+-                # ld if this system was using GNU ld.  Don't know if a
+-                # system like this even exists.
+-                return "-R" + dir
++                # Patched by spack to use gcc syntax by default:
++                return "-Wl,-R" + dir
+ 
+     def library_option(self, lib):
+         return "-l" + lib

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

@@ -92,6 +92,10 @@ class Python(AutotoolsPackage):
     # Patch does not work for Python 3.1
     patch('ncurses.patch', when='@:2.8,3.2:')
 
+    # Ensure that distutils chooses correct compiler option for RPATH on cray:
+    patch('cray-rpath-2.3.patch', when="@2.3:3.0.1 platform=cray")
+    patch('cray-rpath-3.1.patch', when="@3.1:3.99  platform=cray")
+
     _DISTUTIL_VARS_TO_SAVE = ['LDSHARED']
     _DISTUTIL_CACHE_FILENAME = 'sysconfig.json'
     _distutil_vars = None