Enable 64-bit architectures by default for Xcode 5.1 and higher
Enable 64-bit architectures by default for Xcode 5.1 and higher

According to Xcode 5.1 release notes, the "Standard Architectures" build
settings now also include 64-bit architecture, while the build settings
"Standard Architectures Including 64-Bit" is no deprecated.

BUG=gyp:412
R=mark@chromium.org

Review URL: https://codereview.chromium.org/194713003
witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp