[Driver] Refactor interaction between -f(no-)?omit-frame-pointer and...

[Driver] Refactor interaction between -f(no-)?omit-frame-pointer and -m(no-)?omit-leaf-frame-pointer

Use a tri-state enum to represent shouldUseFramePointer() and
shouldUseLeafFramePointer().

This simplifies the logic and fixes PR9825:
  -fno-omit-frame-pointer doesn't imply -mno-omit-leaf-frame-pointer.

and PR24003:
  /Oy- /O2 should not omit leaf frame pointer: this matches MSVC x86-32.
  (/Oy- is a no-op on MSVC x86-64.)

and:
  when CC1 option -mdisable-fp-elim if absent, -momit-leaf-frame-pointer
  can also be omitted.

The new behavior matches GCC:
  -fomit-frame-pointer wins over -mno-omit-leaf-frame-pointer
  -fno-omit-frame-pointer loses out to -momit-leaf-frame-pointer

The behavior makes lots of sense. We have 4 states:

- 00) leaf retained, non-leaf retained
- 01) leaf retained, non-leaf omitted  (this is invalid)
- 10) leaf omitted, non-leaf retained  (what -momit-leaf-frame-pointer was designed for)
- 11) leaf omitted, non-leaf omitted

"omit" options taking precedence over "no-omit" options is the only way
to make 3 valid states representable with -f(no-)?omit-frame-pointer and
-m(no-)?omit-leaf-pointer.

Reviewed By: ychen

Differential Revision: https://reviews.llvm.org/D64294

llvm-svn: 365860