releasetools: Properly handle custom values for tools

Rather than writing these values to their own files, store them
in the target_files META/misc_info.txt. This way, we don't need to
download and parse through multiple files when using signing/release
tools.

Change-Id: I6f845fc055e4ef2ed4adf9628cca505e99b2a9fa
core: arm: Add support for GCC 4.8 and 4.9

Change-Id: I96bffffb4b0e16ef5bcedc85dedc70ca3dc2182f
core: arm: Use -O3 optimization inside TARGET_arm_CFLAGS

Change-Id: I224b62b3dada874d00a90258a1dcffcea09bc029