Fixed bug 4594 - Fix install location of CMake targets on Apple platforms

tschwinger

Followup to #3651

As already noted by Ryan, no framework is being built, so we better install to lib/cmake.

That code was originally part of a patch submitted by David Demelier, whose credit BTW got lost (I combined his patch for #3572 with fixes for #2576 and #3613 resulting in #3651 because things started to depend on another).

I tested that the configuration files are found correctly in the new location on MacOS X based on a hint to the root (see https://cmake.org/cmake/help/latest/command/find_package.html#search-procedure).

CMakeLists.txt

@@ -1831,9 +1831,7 @@ install(TARGETS ${_INSTALL_LIBS} EXPORT SDL2Targets
   RUNTIME DESTINATION bin)
 
 ##### Export files #####
-if (APPLE)
-  set(PKG_PREFIX "SDL2.framework/Resources")
-elseif (WINDOWS)
+if (WINDOWS)
   set(PKG_PREFIX "cmake")
 else ()
   set(PKG_PREFIX "lib/cmake/SDL2")