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/yaml-cpp/package.py

@@ -36,7 +36,7 @@ class YamlCpp(CMakePackage):
 
     variant('shared', default=True,
             description='Enable build of shared libraries')
-    variant('fpic',   default=True,
+    variant('pic',   default=True,
             description='Build with position independent code')
 
     depends_on('boost', when='@:0.5.3')
@@ -49,7 +49,7 @@ def cmake_args(self):
             '-DBUILD_SHARED_LIBS:BOOL=%s' % (
                 'ON' if '+shared' in spec else 'OFF'),
             '-DCMAKE_POSITION_INDEPENDENT_CODE:BOOL=%s' % (
-                'ON' if '+fpic' in spec else 'OFF'),
+                'ON' if '+pic' in spec else 'OFF'),
         ])
 
         return options