Update Windows build for new threading library

MinGW now uses libwinpthread-1.dll instead of pthreadGC2.dll.
To simplify things, create a static executable so users can run fio
from anywhere without needing to copy the dll.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/Makefile b/Makefile
index 8c2c514..3f654f0 100644
--- a/Makefile
+++ b/Makefile
@@ -132,7 +132,7 @@
   SOURCE := $(filter-out engines/mmap.c,$(SOURCE))
   SOURCE += os/windows/posix.c
   LIBS	 += -lpthread -lpsapi -lws2_32
-  CFLAGS += -DPSAPI_VERSION=1 -Ios/windows/posix/include -Wno-format
+  CFLAGS += -DPSAPI_VERSION=1 -Ios/windows/posix/include -Wno-format -static
 endif
 
 OBJS = $(SOURCE:.c=.o)