extras/mac: fix compilation if SDK is not stored in default location

Note that there is nothing wrong with execution on 10.6 if linked against the 10.7 SDK as long as the minimal macosx version is specified correctly

extras/macosx/build-vlc.sh

 #!/bin/sh
 
+OSX_VERSION="10.7"
+SDKROOT=`xcode-select -print-path`/Platforms/MacOSX.platform/Developer/SDKs/MacOSX$OSX_VERSION.sdk
+
 set -e
 
 usage()
@@ -60,6 +63,9 @@ if [ "x$1" != "x" ]; then
     exit 1
 fi
 
+export OSX_VERSION
+export SDKROOT
+
 # Get root dir
 spushd .
 npapi_root_dir=`pwd`
@@ -127,7 +133,6 @@ cd 64build
         --disable-macosx \
         --enable-merge-ffmpeg \
         --disable-growl \
-        --enable-minimal-macosx \
         --enable-faad \
         --enable-flac \
         --enable-theora \
@@ -152,7 +157,7 @@ cd 64build
         --disable-sdl \
         --disable-sdl-image \
         --disable-macosx-vlc-app \
-	--with-macosx-sdk=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.6.sdk \
+	    --with-macosx-sdk=$SDKROOT \
         --with-macosx-version-min=10.6 \
         --prefix=${PREFIX} > ${out}