Avoid calling ParseCommandLineOptions in BackendUtil if possible

Calling `ParseCommandLineOptions` should only be called from `main` as the
CommandLine setup code isn't thread-safe. As BackendUtil is part of the
generic Clang FrontendAction logic, a process which has several threads executing
Clang FrontendActions will randomly crash in the unsafe setup code.

This patch avoids calling the function unless either the debug-pass option or
limit-float-precision option is set. Without these two options set the
`ParseCommandLineOptions` call doesn't do anything beside parsing
the command line `clang` which doesn't set any options.

See also D99652 where LLDB received a workaround for this crash.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D99740