Update SDL2 to version 2.28.1.

libs/SDL2/build-scripts/showrev.sh

@@ -5,10 +5,31 @@
 SDL_ROOT=$(dirname $0)/..
 cd $SDL_ROOT
 
+if [ -e ./VERSION.txt ]; then
+    cat ./VERSION.txt
+    exit 0
+fi
+
+major=$(sed -ne 's/^#define SDL_MAJOR_VERSION  *//p' include/SDL_version.h)
+minor=$(sed -ne 's/^#define SDL_MINOR_VERSION  *//p' include/SDL_version.h)
+micro=$(sed -ne 's/^#define SDL_PATCHLEVEL  *//p' include/SDL_version.h)
+version="${major}.${minor}.${micro}"
+
 if [ -x "$(command -v git)" ]; then
-    rev=$(echo "$(git remote get-url origin 2>/dev/null)@$(git rev-list HEAD~.. 2>/dev/null)")
-    if [ "$rev" != "@" ]; then
-        echo $rev
+    rev="$(git describe --tags --long 2>/dev/null)"
+    if [ -n "$rev" ]; then
+        # e.g. release-2.24.0-542-g96361fc47
+        # or release-2.24.1-5-g36b987dab
+        # or prerelease-2.23.2-0-gcb46e1b3f
+        echo "$rev"
+        exit 0
+    fi
+
+    rev="$(git describe --always --tags --long 2>/dev/null)"
+    if [ -n "$rev" ]; then
+        # Just a truncated sha1, e.g. 96361fc47.
+        # Turn it into e.g. 2.25.0-g96361fc47
+        echo "${version}-g${rev}"
         exit 0
     fi
 fi
@@ -16,10 +37,12 @@ fi
 if [ -x "$(command -v p4)" ]; then
     rev="$(p4 changes -m1 ./...\#have 2>/dev/null| awk '{print $2}')"
     if [ $? = 0 ]; then
-        echo $rev
+        # e.g. 2.25.0-p7511446
+        echo "${version}-p${rev}"
         exit 0
     fi
 fi
 
-echo ""
-exit 1
+# best we can do
+echo "${version}-no-vcs"
+exit 0