Update sdl2.m4 from upstream

m4/sdl2.m4

@@ -9,8 +9,9 @@
 # * also look for SDL2.framework under Mac OS X
 # * removed HP/UX 9 support.
 # * updated for newer autoconf.
+# * (v3) use $PKG_CONFIG for pkg-config cross-compiling support
 
-# serial 2
+# serial 3
 
 dnl AM_PATH_SDL2([MINIMUM-VERSION, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]])
 dnl Test for SDL, and define SDL_CFLAGS and SDL_LIBS
@@ -24,7 +25,7 @@ AC_ARG_WITH(sdl-prefix,[  --with-sdl-prefix=PFX   Prefix where SDL is installed
 AC_ARG_WITH(sdl-exec-prefix,[  --with-sdl-exec-prefix=PFX Exec prefix where SDL is installed (optional)],
             sdl_exec_prefix="$withval", sdl_exec_prefix="")
 AC_ARG_ENABLE(sdltest, [  --disable-sdltest       Do not try to compile and run a test SDL program],
-		    , enable_sdltest=yes)
+                    , enable_sdltest=yes)
 AC_ARG_ENABLE(sdlframework, [  --disable-sdlframework Do not search for SDL2.framework],
         , search_sdl_framework=yes)
 
@@ -54,7 +55,7 @@ AC_ARG_VAR(SDL2_FRAMEWORK, [Path to SDL2.framework])
 
   if test "x$sdl_pc" = xyes ; then
     no_sdl=""
-    SDL2_CONFIG="pkg-config sdl2"
+    SDL2_CONFIG="$PKG_CONFIG sdl2"
   else
     as_save_PATH="$PATH"
     if test "x$prefix" != xNONE && test "$cross_compiling" != yes; then
@@ -70,8 +71,8 @@ AC_ARG_VAR(SDL2_FRAMEWORK, [Path to SDL2.framework])
         sdl_framework=$SDL2_FRAMEWORK
       else
         for d in / ~/ /System/; do
-          if test -d "$dLibrary/Frameworks/SDL2.framework"; then
-            sdl_framework="$dLibrary/Frameworks/SDL2.framework"
+          if test -d "${d}Library/Frameworks/SDL2.framework"; then
+            sdl_framework="${d}Library/Frameworks/SDL2.framework"
           fi
         done
       fi
@@ -192,7 +193,7 @@ int main(int argc, char *argv[])
           echo "*** LD_LIBRARY_PATH environment variable, or edit /etc/ld.so.conf to point"
           echo "*** to the installed location  Also, make sure you have run ldconfig if that"
           echo "*** is required on your system"
-	  echo "***"
+          echo "***"
           echo "*** If you have an old version installed, it is best to remove it, although"
           echo "*** you may also be able to get things to work by modifying LD_LIBRARY_PATH"],
         [ echo "*** The test program failed to compile or link. See the file config.log for the"