Ensure Config.pm has correct setting for cc (#4345)

* Ensure Config.pm has correct setting for cc

Run a filter after install so that Config.pm records the compiler that
Spack built the package with.  If this isn't done, $Config{cc} will be
set to Spack's cc wrapper script.

* Also patch compilers Config_heavy.pl

This patch sets ld=gcc, which appears to work.  I'm not sure if
there's a good way to get at the ld that Spack uses.

* Clean up quoting

* Fix pattern for Config.pm

Does not start at beginning of line...

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

@@ -31,6 +31,7 @@
 # Date: September 6, 2015
 #
 from spack import *
+import os
 
 
 class Perl(Package):  # Perl doesn't use Autotools, it should subclass Package
@@ -160,3 +161,33 @@ def setup_dependent_package(self, module, dependent_spec):
         # if it does not exist already.
         if dependent_spec.package.is_extension:
             mkdirp(module.perl_lib_dir)
+
+    @run_after('install')
+    def filter_config_dot_pm(self):
+        """Run after install so that Config.pm records the compiler that Spack
+        built the package with.  If this isn't done, $Config{cc} will
+        be set to Spack's cc wrapper script.
+        """
+
+        kwargs = {'ignore_absent': True, 'backup': False, 'string': False}
+
+        # Find the actual path to the installed Config.pm file.
+        perl = Executable(join_path(prefix.bin, 'perl'))
+        config_dot_pm = perl('-MModule::Loaded', '-MConfig', '-e',
+                             'print is_loaded(Config)', output=str)
+
+        match = 'cc *=>.*'
+        substitute = "cc => '{cc}',".format(cc=self.compiler.cc)
+        filter_file(match, substitute, config_dot_pm, **kwargs)
+
+        # And the path Config_heavy.pl
+        d = os.path.dirname(config_dot_pm)
+        config_heavy = join_path(d, 'Config_heavy.pl')
+
+        match = '^cc=.*'
+        substitute = "cc='{cc}'".format(cc=self.compiler.cc)
+        filter_file(match, substitute, config_heavy, **kwargs)
+
+        match = '^ld=.*'
+        substitute = "ld='{ld}'".format(ld=self.compiler.cc)
+        filter_file(match, substitute, config_heavy, **kwargs)