cabal: Always process package config files

Drop the check for `libraries != []` in the check for processing the
package config file. Haskell supports empty libraries. In order for
Bazel to support them, we need to process the package config, even for
empty libraries.

Author: iteratee

haskell/private/cabal_wrapper.py

@@ -394,7 +394,7 @@ def make_relative_to_pkgroot(matchobj):
     line = re.sub(re.escape(cfg_execroot) + r'\S*', make_relative_to_pkgroot, line)
     return line
 
-if libraries != [] and os.path.isfile(package_conf_file):
+if os.path.isfile(package_conf_file):
     for lib in libraries:
         os.rename(lib, os.path.join(dynlibdir, os.path.basename(lib)))