build-mingw-w64: Bump to the latest version as of Sep 19th

This brings in a rather large update of the D3D12 header
(d3d12.idl/d3d12.h), which should now be mostly complete and up
to date with the current versions from Microsoft.

build-mingw-w64.sh

@@ -18,7 +18,7 @@ set -e
 
 : ${DEFAULT_WIN32_WINNT:=0x601}
 : ${DEFAULT_MSVCRT:=ucrt}
-: ${MINGW_W64_VERSION:=ddc5b0f6ec4a153485741587885916c8c234da80}
+: ${MINGW_W64_VERSION:=602758b2042bf26978f1a48fd90139b276f18384}
 
 CFGUARD_FLAGS="--enable-cfguard"