windows: use '-l<library>' instead of '<library>.lib' or '-l<library>.lib' which confuses mingw32.
windows: Fix mingw32/debug build.
Debug build failed on mingw32 because CRT assertion disable code was stubbed out.
Replace __declspec(thread) with UV_THREAD_LOCAL which is defined as __thread on GCC.
Merge branch 'win-mingw32-fixes3' of github.com:cjdelisle/libuv