tools: add check-msvcrt.py and check-msvcrt-tre.py for determining which runtime library our deps use.

These were written to help us determine which version of the C runtime
library a given third-party library is linked against in our Windows
build env.

I used this when debugging "defaultlib mismatches" when linking
mumbl.exe, but in the end, I had more luck using link.exe's
/verbose flag to debug that particular case.

Note: these scripts don't always work, because not all libs seem to embed
/defaultlib directives. However, it might still be useful in an
automated vetting/sanity script that can be performed after a successful
buildenv build.