build-mingw-w64: Bump to the latest version as of Sep 17th

This is the latest version, minus one commit.

The very latest commit, 20331109d1c90c19a510408ab119a76004bc41ea,
causes issues with compiling VLC; that is a VLC issue (redefining
GUIDs that now are provided by the system headers), but holding
off of that change until VLC is updated to cope with it.

Author: mstorsjo

build-mingw-w64.sh

@@ -18,7 +18,7 @@ set -e
 
 : ${DEFAULT_WIN32_WINNT:=0x601}
 : ${DEFAULT_MSVCRT:=ucrt}
-: ${MINGW_W64_VERSION:=1b554dec06f8d3c26b856a7d1575f396d8ffa403}
+: ${MINGW_W64_VERSION:=b70f2474437017368c99ca202809f20c4f773855}
 
 CFGUARD_FLAGS="--enable-cfguard"