This reworks the force-frame-pointer PR to explicitly only consider the
value of the flag if it is provided, and use a target default otherwise.
Something that was tried but not kept was renaming the flag to
`frame-pointer`, because for flag `frame-pointer=no`, there is no
guarante, that LLVM will elide *all* the frame pointers; oposite of what
the literal reading of the flag would suggest.
We apparently used to generate bad/incomplete debug info causing
debuggers not to find symbols of stack allocated variables. This was
somehow worked around by having frame pointers.
With the current codegen, this seems no longer necessary, so we can
remove the code that force-enables frame pointers whenever debug info
is requested.
Since certain situations, like profiling code profit from having frame
pointers, we add a -Cforce-frame-pointers flag to always enable frame
pointers.
Fixes#11906
