macosx/framework: Make sure base SDK is set to 10.5.

This should fix the issue about libmad when build the framework with the default settings.

VLCKit.xcodeproj/project.pbxproj

@@ -695,7 +695,7 @@
 				GCC_WARN_UNUSED_VARIABLE = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				PREBINDING = NO;
-				SDKROOT = "";
+				SDKROOT = macosx10.5;
 			};
 			name = Debug;
 		};
@@ -709,7 +709,7 @@
 				GCC_WARN_UNUSED_VARIABLE = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				PREBINDING = NO;
-				SDKROOT = "";
+				SDKROOT = macosx10.5;
 			};
 			name = Release;
 		};