Github CI/CD updates

- Nuke and reinstall HomeBrew for macOS builds. Gets around the whole
  problem of stale links and conflicting packages installed in the GitHub
  macOS images.

- macOS 12 and Ubuntu 20.04 officially deprecated. Ubuntu 20.04 will be
  removed from GitHub's runner images on 01 APR 2025.

- .travis/deps.sh: Add mingw32 as a dependency target, enable MinGW64
  32-bit builds.

- Work around LTO bug on Ubuntu and macOS compilers, where LTO appears
  to miscalculate the number of bytes stored when using the default byte
  swapping 'for' loop. This is a workaround that uses compiler swapping
  intrinsics for well known sizes that appeases LTO. The alternative is
  to wait for a compiler fix, which is infeasible.

.travis/deps.sh

@@ -27,7 +27,20 @@ install_linux() {
     sudo apt-get install -ym libegl1-mesa-dev libgles2-mesa-dev
     sudo apt-get install -ym libsdl2-dev libfreetype6-dev libsdl2-ttf-dev
     sudo apt-get install -ym libpcap-dev libvdeplug-dev
-    sudo apt-get install -ym cmake cmake-data
+    sudo apt-get install -ym cmake cmake-data ninja-build
+}
+
+install_mingw32() {
+    ## Doesn't have libpcap or cmake's extra modules. Not that this
+    ## makes much of a difference.
+    pacman -S --needed mingw-w64-i686-ninja \
+	mingw-w64-i686-cmake \
+        mingw-w64-i686-gcc \
+	mingw-w64-i686-make \
+        mingw-w64-i686-pcre \
+	mingw-w64-i686-freetype \
+        mingw-w64-i686-SDL2 \
+	mingw-w64-i686-SDL2_ttf
 }
 
 install_mingw64() {
@@ -71,14 +84,15 @@ install_clang64() {
 
 
 case "$1" in
-  osx|macports|linux|mingw64|ucrt64|clang64)
+  osx|macports|linux|mingw32|mingw64|ucrt64|clang64)
     install_"$1"
     ;;
   arch-linux)
     install_arch_linux
     ;;
   *)
-    echo "$0: Need an operating system name: osx, arch-linux, linux, mingw64 or ucrt64"
+    echo "$0: Need an operating system name:"
+    typeset -f | sed -e '/^install_/!d' -e 's/^install_/  - /' -e 's/ ()//' | sort
     exit 1
     ;;
 esac