Clean up compiler optimization variable FULL_OPTIMIZATION

Clean up compiler optimization variable FULL_OPTIMIZATION

In bitbake.conf, remove FULL_OPTIMIZATION, set "-O2 ${DEBUG_LEVELFLAG}"
to SELECTED_OPTIMIZATION directly

In mesa.inc, due to llvmpipe is slow if compiled with
-fomit-frame-pointer (e.g. -O2), set -fno-omit-frame-pointer
to TARGET_CFLAGS only if option -O2 existed

Correct typo in clang.patch

In recipe harfbuzz, use SELECTED_OPTIMIZATION to instead of
FULL_OPTIMIZATION

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>