configure: don't warn SDL abi if disabled

SDL has the same problem as GTK that we might get warnings on SDL ABI
version even if SDL is disabled.  Fix that by only probing SDL if SDL is
enabled.  Also this should let configure be a little bit faster since we
don't really need to probe SDL stuff when it's off.

CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Gerd Hoffmann <kraxel@redhat.com>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Daniel P. Berrange <berrange@redhat.com>
CC: Fam Zheng <famz@redhat.com>
CC: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20180410054034.20479-1-peterx@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/configure b/configure
index 931d2a0..0a19b03 100755 (executable)
--- a/configure
+++ b/configure
@@ -2835,49 +2835,52 @@ fi
 # Look for sdl configuration program (pkg-config or sdl-config).  Try
 # sdl-config even without cross prefix, and favour pkg-config over sdl-config.
 
-if test "$sdlabi" = ""; then
-    if $pkg_config --exists "sdl2"; then
-        sdlabi=2.0
-    elif $pkg_config --exists "sdl"; then
-        sdlabi=1.2
-    else
-        sdlabi=2.0
-    fi
-fi
+sdl_probe ()
+{
+  sdl_too_old=no
+  if test "$sdlabi" = ""; then
+      if $pkg_config --exists "sdl2"; then
+          sdlabi=2.0
+      elif $pkg_config --exists "sdl"; then
+          sdlabi=1.2
+      else
+          sdlabi=2.0
+      fi
+  fi
 
-if test $sdlabi = "2.0"; then
-    sdl_config=$sdl2_config
-    sdlname=sdl2
-    sdlconfigname=sdl2_config
-elif test $sdlabi = "1.2"; then
-    sdlname=sdl
-    sdlconfigname=sdl_config
-else
-    error_exit "Unknown sdlabi $sdlabi, must be 1.2 or 2.0"
-fi
+  if test $sdlabi = "2.0"; then
+      sdl_config=$sdl2_config
+      sdlname=sdl2
+      sdlconfigname=sdl2_config
+  elif test $sdlabi = "1.2"; then
+      sdlname=sdl
+      sdlconfigname=sdl_config
+  else
+      error_exit "Unknown sdlabi $sdlabi, must be 1.2 or 2.0"
+  fi
 
-if test "$(basename $sdl_config)" != $sdlconfigname && ! has ${sdl_config}; then
-  sdl_config=$sdlconfigname
-fi
+  if test "$(basename $sdl_config)" != $sdlconfigname && ! has ${sdl_config}; then
+    sdl_config=$sdlconfigname
+  fi
 
-if $pkg_config $sdlname --exists; then
-  sdlconfig="$pkg_config $sdlname"
-  sdlversion=$($sdlconfig --modversion 2>/dev/null)
-elif has ${sdl_config}; then
-  sdlconfig="$sdl_config"
-  sdlversion=$($sdlconfig --version)
-else
-  if test "$sdl" = "yes" ; then
-    feature_not_found "sdl" "Install SDL2-devel"
+  if $pkg_config $sdlname --exists; then
+    sdlconfig="$pkg_config $sdlname"
+    sdlversion=$($sdlconfig --modversion 2>/dev/null)
+  elif has ${sdl_config}; then
+    sdlconfig="$sdl_config"
+    sdlversion=$($sdlconfig --version)
+  else
+    if test "$sdl" = "yes" ; then
+      feature_not_found "sdl" "Install SDL2-devel"
+    fi
+    sdl=no
+    # no need to do the rest
+    return
+  fi
+  if test -n "$cross_prefix" && test "$(basename "$sdlconfig")" = sdl-config; then
+    echo warning: using "\"$sdlconfig\"" to detect cross-compiled sdl >&2
   fi
-  sdl=no
-fi
-if test -n "$cross_prefix" && test "$(basename "$sdlconfig")" = sdl-config; then
-  echo warning: using "\"$sdlconfig\"" to detect cross-compiled sdl >&2
-fi
 
-sdl_too_old=no
-if test "$sdl" != "no" ; then
   cat > $TMPC << EOF
 #include <SDL.h>
 #undef main /* We don't want SDL to override our main() */
@@ -2919,6 +2922,10 @@ EOF
     fi
     sdl=no
   fi # sdl compile test
+}
+
+if test "$sdl" != "no" ; then
+  sdl_probe
 fi
 
 if test "$sdl" = "yes" ; then