Optimize load inline via pch (#106696)
Add PreCompiled Header(PCH) to reduce load_inline build time.
PCH is gcc built-in mechanism: https://gcc.gnu.org/onlinedocs/gcc-4.0.4/gcc/Precompiled-Headers.html
Add PCH for '#include <torch/extension.h>'. This file will used in all load_inline modules. All load_inline modules can take benifit from this PR.
Changes:
1. Add PCH signature to guarantee PCH(gch) file take effect.
2. Unification get cxx compiler funtions.
3. Unification get build flags funtions.
Before this PR:
Added this PR:
Compiling time is reduced from 14.06s to 7.36s.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106696
Approved by: https://github.com/jgong5, https://github.com/jansel
