I see from test/test2/Makefile that 24_math_library is removed for Windows because of lack of round().
SKIP += 24_math_library.test # don't have round()
With mob compiled with a recent MinGW gcc compiler.
This test is fully working. Can you reconsider to add it as part of standard tests suite.
I also note that 28_strings is removed because Windows lacks index/rindex (which is true).
Now, if you remove <strings.h> which was a BSDish include now removed from POSIX and replace
printf("%s\n", index(a, 'o'));
printf("%s\n", rindex(a, 'l'));
printf("%d\n", rindex(a, 'x') == NULL);
By iso C equivalent functions:
printf("%s\n", strchr(a, 'o'));
printf("%s\n", strrchr(a, 'l'));
printf("%d\n", strrchr(a, 'x') == NULL);
It works on Windows and should work on any system.