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/hdf/package.py

@@ -51,7 +51,7 @@ def configure_args(self):
         spec = self.spec
 
         config_args = [
-            'CFLAGS=-fPIC',
+            'CFLAGS={0}'.format(self.compiler.pic_flag),
             '--with-jpeg={0}'.format(spec['jpeg'].prefix),
             '--with-zlib={0}'.format(spec['zlib'].prefix),
             '--disable-netcdf',  # must be disabled to build NetCDF with HDF4