Support -Wno-frame-larger-than (with no =) and make it properly
interoperate with -Wframe-larger-than. Reject -Wframe-larger-than with
no argument.
We continue to support Clang's old spelling, -Wframe-larger-than=, for
compatibility with existing users of that facility.
In passing, stop the driver from accepting and ignoring
-fwarn-stack-size and make it a cc1-only flag as intended.
-Wframe-larger-than= is an interesting warning; we can't know the frame
size until PrologueEpilogueInsertion (PEI); very late in the compilation
pipeline.
-Wframe-larger-than= was propagated through CC1 as an -mllvm flag, then
was a cl::opt in LLVM's PEI pass; this meant it was dropped during LTO
and needed to be re-specified via -plugin-opt.
Instead, make it part of the IR proper as a module level attribute,
similar to D103048. Introduce -fwarn-stack-size CC1 option.
Reviewed By: rsmith, qcolombet
Differential Revision: https://reviews.llvm.org/D103928
Richard Smith