Lower unfolding threshold for windows (again.)

We creeped back up again past the symbol threshold on my test x86_64
win2k8 test machine. This brings it down to 60600 symbols in split
windows DLL.

Signed-off-by: Austin Seipp <austin@well-typed.com>

mk/config.mk.in

@@ -105,7 +105,7 @@ endif
 #
 # See #5987
 ifeq "$(TargetOS_CPP)" "mingw32"
-GhcStage2HcOpts += -funfolding-creation-threshold=300
+GhcStage2HcOpts += -funfolding-creation-threshold=100
 endif
 
 # Some platforms don't support shared libraries