Add visibility flag to GYP.

BUG=

Review URL: https://codereview.webrtc.org/1826453004

Cr-Commit-Position: refs/heads/master@{#12108}

webrtc/build/common.gypi

@@ -141,6 +141,12 @@
     # Enabling this may break interop with Android clients that support H264.
     'use_objc_h264%': 0,
 
+    # Enable this to prevent extern symbols from being hidden on iOS builds.
+    # The chromium settings we inherit hide symbols by default on Release
+    # builds. We want our symbols to be visible when distributing WebRTC via
+    # static libraries to avoid linker warnings.
+    'ios_override_visibility%': 0,
+
     # Determines whether QUIC code will be built.
     'use_quic%': 0,
 
@@ -380,6 +386,12 @@
           'WEBRTC_IOS',
         ],
       }],
+      ['OS=="ios" and ios_override_visibility==1', {
+        'xcode_settings': {
+          'GCC_INLINES_ARE_PRIVATE_EXTERN': 'NO',
+          'GCC_SYMBOLS_PRIVATE_EXTERN': 'NO',
+        }
+      }],
       ['OS=="ios" and use_objc_h264==1', {
         'defines': [
           'WEBRTC_OBJC_H264',

webrtc/build/ios/build_ios_libs.sh

@@ -57,7 +57,7 @@ function build_webrtc {
     FLAVOR="${FLAVOR}-iphonesimulator"
   fi
   export GYP_DEFINES="OS=ios target_arch=${TARGET_ARCH} use_objc_h264=1 \
-clang_xcode=1"
+clang_xcode=1 ios_override_visibility=1"
   export GYP_GENERATORS="ninja"
   export GYP_GENERATOR_FLAGS="output_dir=${OUTPUT_DIR}"
   webrtc/build/gyp_webrtc webrtc/build/ios/merge_ios_libs.gyp