shared/utils: don't warn of unknown warning disables with clang

When pushing a warning disable with clang, always disable
-Wunknown-warning-option first -- it might be that clang wouldn't warn
of what we're trying to disable because it doesn't recognize it in the
first place. That is entierely okay.

With clang-5.0.0:

    CC       libnm/tests/libnm_tests_test_secret_agent-test-secret-agent.o
  In file included from libnm/tests/test-secret-agent.c:29:
  In file included from ./shared/nm-test-libnm-utils.h:23:
  ./shared/nm-utils/nm-test-utils.h:432:3: error: unknown warning group '-Wunused-but-set-variable', ignored [-Werror,-Wunknown-warning-option]
                  NM_PRAGMA_WARNING_DISABLE("-Wunused-but-set-variable")
                  ^
  ./shared/nm-utils/nm-macros-internal.h:223:9: note: expanded from macro 'NM_PRAGMA_WARNING_DISABLE'
          _Pragma(_NM_PRAGMA_WARNING_DO(warning))
          ^
  <scratch space>:204:25: note: expanded from here
   GCC diagnostic ignored "-Wunused-but-set-variable"
                          ^
  1 error generated.

(cherry picked from commit fc4552d3912f2fc99690c6d0c08cb7f16c6d336f)

1 files changed, 1 insertions, 0 deletions

diff --git a/shared/nm-utils/nm-macros-internal.h b/shared/nm-utils/nm-macros-internal.h
index fb8d3f5840..5bcc34b420 100644
--- a/shared/nm-utils/nm-macros-internal.h
+++ b/shared/nm-utils/nm-macros-internal.h
@@ -161,6 +161,7 @@ _nm_auto_protect_errno (int *p_saved_errno)
 #elif defined (__clang__)
 #define NM_PRAGMA_WARNING_DISABLE(warning) \
         _Pragma("clang diagnostic push") \
+        _Pragma(_NM_PRAGMA_WARNING_DO("-Wunknown-warning-option")) \
         _Pragma(_NM_PRAGMA_WARNING_DO(warning))
 #else
 #define NM_PRAGMA_WARNING_DISABLE(warning)