Add "dumpmachine"/"dumpmachinefull" arguments to get the target machine triplet ("dumpmachinefull" for the full MSVC version).

[falhumai96]

Recreated the pull request from #14, as I needed to change the source branch in my fork.

Add two new command-line arguments to get the target machine's triplet, by parsing the command-line output of cl:
* dumpmachine, which is to get the base machine triplet in the format {arch}-pc-windows-msvc, where {arch} is the target archetecture. If the target architecture is ARM or X86, {arch} will be set to armv7 or i386, respectfully (since there are many ARM or X86 archetectures). dumpmachine is similer to that of gcc/clang's command of the same name.
* dumpmachinefull, which has the same output as dumpmachine, except it is post-fixed by the full MSVC version being used. In other words, the command-line argument has the following format {arch}-pc-windows-msvc{msvcver}, where {arch} is the target archetecture and {msvcver} is the MSVC version.

These arguments precede any other arguments passed to cccl, and if dumpmachine/dumpmachinefull is processed, it will print the target triplet and exit succefully (the first of dumpmachine or dumpmachinefull will be processed).

[falhumai96]

@vadz @wsfulton I dropped the last PR and recreated it because I needed to change the source branch from falhumai96:master to falhumai96:implement-dumpmachine, as I have another incoming change 😀.

Anyhow, @wsfulton, what do you mean by documentation from #14 (comment)? I added some comments above my code implementation to indicate the purpose of the command-line arguments.