[PATCH, PR43920] Improve code-size optimizations

[Tom de Vries]

This patch set fixes PR 43920 - 'Choosing conditional execution over
conditional branches for code size in some cases'.

The patch set was tested on ARM and x86_64. The codesize changes were
benchmarked for ARM Thumb-2. For SPEC2000 and EEMBC CoreMark, a
reduction of 1.1% in the geomean of the benchmark sizes was measured.
For pic code, the reduction was 1.0%.

Patches will be posted separately.

Thanks,
- Tom