Fixed showrev.sh when using the Bourne shell

build-scripts/showrev.sh

@@ -7,7 +7,7 @@ cd $SDL_ROOT
 
 if [ -x "$(command -v hg)" ]; then
     rev="$(hg parents --template 'hg-{rev}:{node|short}' 2>/dev/null)"
-    if [ "$?" == 0 ]; then
+    if [ $? = 0 ]; then
         echo $rev
         exit 0
     fi
@@ -15,7 +15,7 @@ fi
 
 if [ -x "$(command -v p4)" ]; then
     rev="$(p4 changes -m1 ./...\#have 2>/dev/null| awk '{print $2}')"
-    if [ "$?" == 0 ]; then
+    if [ $? = 0 ]; then
         echo $rev
         exit 0
     fi