Add patch to fix duplicate symbol of webrtc and libjingle.

duplicate symbol __Z35p_convertHostCFStringRefToCPPStringPK10__CFStringRSs in:
  libjingle.a(libjingle.macconversion.o)
  libwebrtc_base.a(webrtc_base.macconversion.o)
duplicate symbol __Z22p_convertCFNumberToIntPK10__CFNumberPi in:
  libjingle.a(libjingle.macconversion.o)
  libwebrtc_base.a(webrtc_base.macconversion.o)
duplicate symbol __Z16p_isCFNumberTruePK10__CFNumber in:
  libjingle.a(libjingle.macconversion.o)
  libwebrtc_base.a(webrtc_base.macconversion.o)
ld: 3 duplicate symbols for architecture x86_64

patches/third_party/webrtc/macconversion.patch

@@ -0,0 +1,12 @@
+diff --git a/base/base.gyp b/base/base.gyp
+index 330ea82..69a9b01 100644
+--- a/base/base.gyp
++++ b/base/base.gyp
+@@ -136,7 +136,6 @@
+         'maccocoasocketserver.mm',
+         'maccocoathreadhelper.h',
+         'maccocoathreadhelper.mm',
+-        'macconversion.cc',
+         'macconversion.h',
+         'macsocketserver.cc',
+         'macsocketserver.h',