build: disable openssl build warnings on macos

We already disable `-Wmissing-field-initializers` on other Unices but
not on MacOS.

PR-URL: nodejs#19046
Fixes: nodejs#18983
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>

deps/openssl/openssl.gyp

@@ -157,6 +157,9 @@
       }, {
         'defines': ['<@(openssl_default_defines_not_win)'],
         'cflags': ['-Wno-missing-field-initializers'],
+        'xcode_settings': {
+          'WARNING_CFLAGS': ['-Wno-missing-field-initializers'],
+        },
         'conditions': [
           ['OS=="mac"', {
             'defines': ['<@(openssl_default_defines_mac)'],