Define TARGET_GCC_VERSION in target specific make files.

So that GCC refresh can be performed in a target specific way.

Change-Id: I867e8b8fd671bef8c5af300e657a6da4fface032
Enable lunch command to pick up new toolchain version.

Otherwise the previously exported value will be sticky and the value
defined in the TARGET makefile is ignored.

Change-Id: Icdacb8c46034b8a24a9875b7596b31d00861512a
Link libgcc.a before shared libraries (especially libc.so).

[cherry-picked from internal master]

Change-Id: I53d19754d0d40e9ca2f3d043001cc77e39e5d795