[gyp] Disable compiler warning

It's disabled in gn and on several platforms, so also disable it for
linux systems in general.

R=machenbach@chromium.org

Change-Id: Id5d0e5d30cc27c449d05352df6dd0aade5d9e6fd
Reviewed-on: https://chromium-review.googlesource.com/640708Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47677}

gypfiles/standalone.gypi

@@ -754,7 +754,7 @@
           '-Wno-unused-parameter',
           '-pthread',
           '-pedantic',
-          '-Wmissing-field-initializers',
+          '-Wno-missing-field-initializers',
           '-Wno-gnu-zero-variadic-macro-arguments',
         ],
         'cflags_cc': [