Add libs attribute to mesa and mesa-glu packages (#8904)

Also fix dependency version in glvis package.
Fixes build errors mentioned in #8454.

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

@@ -80,9 +80,6 @@ def fetcher(self):
         of OpenGL your Mac uses."""
         raise InstallError(msg)
 
-    def install(self, spec, prefix):
-        pass
-
     @property
     def libs(self):
         for dir in ['lib64', 'lib']:
@@ -90,4 +87,3 @@ def libs(self):
                                   shared=True, recursive=False)
             if libs:
                 return libs
-        return None