[flang] [llvm] [flang][flang-rt] Add support for non-standard TIMEF intrinsic (PR #185377)

[Kelvin Li via llvm-commits]

kkwli wrote:

The XLF also supports `timef` that returns millisecond instead of second. The function uses mutex to ensure its thread-safety.

https://www.ibm.com/docs/en/openxl-fortran-aix/17.1.4?topic=procedures-timef

https://github.com/llvm/llvm-project/pull/185377