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/netcdf/package.py

@@ -133,7 +133,7 @@ def configure_args(self):
             config_args.append('--disable-shared')
             # We don't have shared libraries but we still want it to be
             # possible to use this library in shared builds
-            CFLAGS.append('-fPIC')
+            CFLAGS.append(self.compiler.pic_flag)
 
         if '+dap' in spec:
             config_args.append('--enable-dap')