The naming convention for submodule files varies across compilers. Add
a table to the compiler information modules and thread the information
through to the Fortran module dependency parser. Fill out the table for
compiler ids known to support Fortran submodules.
Fixes: #18746
Running flang with `-E` now ignores any `-o` option and always prints
preprocessed output to stdout. Use shell redirection to place it in a
file instead.
Fixes: #18497
flang is a Fortran compiler built on top of clang [1]. Because flang
shares a lot of commonalities with clang, the flang module piggybacks
off the clang module and overrides certain options.
Add flang to Fortran compiler auto find list.
Update flang preprocessor macros to differentiate from PGI.
Add Flang-FindBinUtils.
[1] https://github.com/flang-compiler/flang
