Fix win32 support header for mingw32.

These functions are defined as static in the mingw32 headers.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@219140 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 4c888397167ac6b3c6a88987dc5823aa13bba7e7)
Change-Id: I2b86609d223a501dff162552f3e2408424eeaf3a
1 file changed