build: Prefix version from git with SDL- rather than SDL3-

We can tell it's SDL 3 from the version number and git revision,
so there's no need to duplicate that in the prefix.

Signed-off-by: Simon McVittie <smcv@collabora.com>
(cherry picked from commit d5b79418f4822284ef6cd9d7e6d52b7b27a11328)

CMakeLists.txt

@@ -3160,7 +3160,7 @@ endif()
 if(NOT SDL_REVISION)
   # If SDL_REVISION is not overrided, use git to describe
   git_describe(SDL_REVISION_GIT)
-  set(SDL_REVISION "SDL3-${SDL3_VERSION}-${SDL_REVISION_GIT}")
+  set(SDL_REVISION "SDL-${SDL3_VERSION}-${SDL_REVISION_GIT}")
 endif()
 
 execute_process(COMMAND "${CMAKE_COMMAND}" -E make_directory "${SDL3_BINARY_DIR}/include-revision/SDL3")