Add lint-makefiles Makefile linting test.

We add a 'make check' test that lints all Makefiles in the source
directory of the glibc build. This linting test ensures that the
lines in all Makefiles will be sorted correctly as developers
creates patches.  It is added to 'make check' because it is
light-weight and supports the existing developer workflow

The test adds ~3s to a 'make check' execution.

No regressions on x86_64 and i686.

Reviewed-by: Florian Weimer <fweimer@redhat.com>