Added m4 option to BUILD_PREBUILT

It will copy files to the target location using the m4 macro
preprocessor. Three predefined macros are available:

ONLY_IN_PRODUCT(product name, text to be included if product)
ONLY_IN_VARIANT(variant name, text to be included if variant)
ONLY_IN_DEBUG(text to be included if eng or userdebug)

Change-Id: If2a73d1b2812117eeef7ca2f9a3f789a3b9070d3