[cmake] By default do not build compiler-rt with PGO
Patch by Zhizhou Yang!
In his own words:
Currently compiler-rt doesn't officially support either PGO
instrumentation or use PGO profdata to build it.
PGO related flags are passed into compiler-rt since rL372209, and
causing bugs: 45022, crbug:1018840
This patch adds several checks in compiler-rt to disable PGO related
flags and provides a flag to turn on PGO for compiler-rt if needed.
Differential Revision: https://reviews.llvm.org/D75499