Add MINGW32_NT checks for test Makefiles (see #240).

[landofcake]

Add checks for MINGW32_NT to filter-test2 and shared_lib test Makefiles and set BASE_OS to MSYS_NT.

[codecov]

Codecov Report

Merging #241 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #241   +/-   ##
=======================================
  Coverage   87.37%   87.37%           
=======================================
  Files          12       12           
  Lines        1339     1339           
  Branches      243      243           
=======================================
  Hits         1170     1170           
  Misses        115      115           
  Partials       54       54

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update dfb74bd...0b6dfed. Read the comment docs.

[latk]

Looks great! Thank you for working through all those errors to get the tests working on your Windows.

Under which name would you like to be credited in the AUTHORS file? If you don't specify any preference, I'll use your Github user name.

[landofcake]

I'm sorry @latk , I forgot to put my name in my github profile (Dave George), I've now added it so go ahead and use that. Thanks!