Prepare upcoming GCC 4.8 release.

o Add -Wno-unused-parameter -Wno-unused-but-set-parameter to suppress
  new warnings.
o Define GCC_COLORS to enable colorful diagnostic messages.

Change-Id: Icbd62300b0e6f39d4e514edec2431a06b4d72421
(cherry picked from internal commit ccd8e6082b5b1e519a75068fa6c887a1a85b53c4)
Add missing LOCAL_ADDITIONAL_DEPENDENCIES dependency to BUILD_PREBUILT.

Change-Id: Id7c0e77110653e618d783026cd4b4aeadb3c45ec
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
mkbootimg: Support custom mkbootimg implementation

Support using custom mkbootimg to allow boards to specify custom
boot image formats. Also export this as the environment variable
MKBOOTIMG to the *_from_target_files releasetools scripts.

Change-Id: I2084273b1175de097fb7da5c4f2264ea8014d74f
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>