[Feature request] Optional pass AR and RANLIB implementation

[band-a-prend]

The Builder.py has hardcoded archiver+flags and ranlib implementation:

link_cmd = "ar -rcs " + lib + " " + link_cmd + " \n ranlib " + lib

that makes imposible to use other implementation of them, e.g. on built of StringiFor.

Is it possible to add optional passing of ar_cmd and ranlib_cmd to pass e.g. llvm-ar and llvm-ranlib executables as string parameter?

Maybe it could be the additional options for custom as compiler -fc like -ar my_ar ar_flags and -rl my_ranlib?

Although the llvm fortran compiler has no own driver and use external compiler to produce executable.