Remove $(shell) from Makefile

Move clang version extraction logic to a short shell script, where we'll
do this parsing only when it needs to be updated. Right now we're
executing this $(shell) 28 times every time 'make' is run, even if we
don't need to reparse the Android.mk files.

Test: generated Version.inc is identical before and after this change.
Change-Id: I37381baed1a66f4487c2675c1de75302767350ed
2 files changed