Switch optimization cflag to late-resolve the debug_optimize and release_optimize vars.

Switch optimization cflag to late-resolve the debug_optimize and release_optimize vars.

This will allow lower-level targets to change their desired optimization level.  In particular, the ffmpeg build requires this because it has problems compiling with -O0.

BUG=22307
TEST=none

[awong, 2009-10-24 02:16:50]

Here's the late resolution change.

Running through try servers, and going to do a test build on my box. Won't
submit if anything goes wrong.

[Mark Mentovai, 2009-10-24 03:56:19]

http://www.lge.com/us/

[Timur Iskhodzhanov, 2009-10-27 06:35:55]

This change might have affected Valgrind/ThreadSanitizer bots as they support
"-O1 -g -fno-inline -fno-omit-frame-pointer -fno-builtin" as the maximum
optimization level.
I'll investigate whether this is the case and file a bug issue if appropriate.