Switch Windows build to 64bit binaries

Use the x86_64 compiler instead of i686 and use the version that uses
UCRT runtime. This is available by default on Windows 10 or newer and
can be installed on older OSes too.

.github/workflows/build.yml

@@ -47,9 +47,9 @@ jobs:
     - name: Setup MSYS2 environment
       uses: msys2/setup-msys2@v2
       with:
-        msystem: MINGW32
+        msystem: UCRT64
         update: true
-        install: mingw-w64-i686-gcc automake autoconf pkg-config make zip mingw-w64-i686-poppler mingw-w64-i686-wxWidgets
+        install: mingw-w64-ucrt-x86_64-gcc automake autoconf pkg-config make zip mingw-w64-ucrt-x86_64-poppler mingw-w64-ucrt-x86_64-wxWidgets
 
     - name: Bootstrap
       run: ./bootstrap

win32/collect-dlls.sh

@@ -31,8 +31,8 @@ while true ; do
 
     cat $OUTPUT/*.objdeps | sort | uniq | while read i ; do
         dll=`echo $i`  # fixup weird line endings
-        if [[ -f /mingw32/bin/$dll ]] ; then
-            add_binary /mingw32/bin/$dll
+        if [[ -f /ucrt64/bin/$dll ]] ; then
+            add_binary /ucrt64/bin/$dll
         fi
     done
 done