Xcode: Add extra '$(inherited)' entries using InheritBuildSettingAttribute.
Add extra '$(inherited)' entries using InheritBuildSettingAttribute. These have been added to:
- GCC_PREPROCESSOR_DEFINITIONS
- OTHER_CFLAGS
- OTHER_LDFLAGS
This is to allow Cocoapods to work correctly as it uses xcconfig files to alter build settings in Xcode, and requires these build settings to inherit from their parent, not overwrite.