Changed every 'fpic' variant to 'pic' (#4969)

* Changed every 'fpic' variant to 'pic'. fixes #2463

Every variant that activates compilation of position independent code
has been changed to 'pic'. Hardcoded compiler flags in packages have
been substituted with `self.compiler.pic_flag`.

* Changed literal uses of '-fpic' to 'self.compiler.pic_flag'

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

@@ -91,7 +91,7 @@ def install(self, spec, prefix):
             raise InstallError('METIS@:4 does not support the following '
                                'variants: gdb, int64, real64.')
 
-        options = ['COPTIONS=-fPIC']
+        options = ['COPTIONS={0}'.format(self.compiler.pic_flag)]
         if '+debug' in spec:
             options.append('OPTFLAGS=-g -O0')
         make(*options)
@@ -119,7 +119,7 @@ def install(self, spec, prefix):
             install(sharefile, prefix.share)
 
         if '+shared' in spec:
-            shared_flags = ['-fPIC', '-shared']
+            shared_flags = [self.compiler.pic_flag, '-shared']
             if sys.platform == 'darwin':
                 shared_suffix = 'dylib'
                 shared_flags.extend(['-Wl,-all_load', 'libmetis.a'])