Build Android Framework host library on Mac

Based on ag/5616352, patch set 5.

Bug: b/118742766
Test: lunch sdk && mmma external/skia on Mac

Similar to the linux build, use a new set of GN arguments to create a
json object to fill in the updated template.

Add the new include/config/mac folder for the newly generated mac-
specific SkUserConfig.h.

Include stdarg.h in SkTraceEventCommon, which is necessary for the mac
build.

Add a new GN arg (skia_use_fonthost_mac) to allow framework build to
manually not build SkFontHost_mac.cpp, and use the same font host
as the other builds.

Change-Id: I654ba496306a3f3591c3937ad5524cd45e49dd65
Reviewed-on: https://skia-review.googlesource.com/c/173183
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
3 files changed