build-mingw-w64: Update to the latest version

This contains new declarations that the latest version of llvm
requires, when building llvm for windows on aarch64.

Notable changes are:
- Fixed compatibility fallbacks for running libc++ on Windows 7
- Improved handling of multibyte functions with UCRT
- Fixed installing mingw-w64-crt and widl in paths that contain spaces
- Fixed sscanf with double output on arm/aarch64
- Improved math functions, in particular for arm/aarch64

build-mingw-w64.sh

@@ -4,7 +4,7 @@ set -e
 
 : ${DEFAULT_WIN32_WINNT:=0x601}
 : ${DEFAULT_MSVCRT:=ucrt}
-: ${MINGW_W64_VERSION:=0a1d495478d8ed1a94fc77b9dbb428b7e0372588}
+: ${MINGW_W64_VERSION:=49e9a673b36a1241747bf3ea95d040f127753f81}
 unset HOST
 
 while [ $# -gt 0 ]; do