Revert "MinGW provides random() in -liberty, no need to replace it"

Revert "MinGW provides random() in -liberty, no need to replace it"

This reverts commit 3ec807e99a8dfa6094660896d17bf20dd92e0de8.

Our nightly build test cases rely on the PRN sequence generated by GNU
libc's random().  We used to have such a PRNG in our tree (derived
from an old version of GNU libc's), for use under Windows.  Thus we
got the same PRN sequence on both our nightly test systems.  Commit
3ec807e9 switched to -liberty under Windows and removed our random().
Now we got a different sequence there, breaking the test cases.

Test cases still don't work on non-Windows systems where random()
doesn't match GNU libc's.  We should switch to a PRNG that produces
the same sequence everywhere.

Conflicts:

	src/lib/w32/w32misc.h