* Define ANGLE_PLATFORM_WINDOWS instead of _WIN32. * Add arm64 target for mingw toolchain gn file. * Use -msse3 flag for x86 and x86_64 only.
* Define ANGLE_PLATFORM_WINDOWS instead of _WIN32. * Add arm64 target for mingw toolchain gn file. * Use -msse3 flag for x86 and x86_64 only.