sdl12-compat: cmake: make dylib versions overridable (thanks Dominik Reichardt.)

SDL Commits
1 
From ba4c1749d2e846f91886f37cbc9306003013662d Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Mon, 7 Jun 2021 14:29:10 +0300
Subject: [PATCH] cmake: make dylib versions overridable (thanks Dominik
 Reichardt.)

---
 CMakeLists.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6256c3a..2231d1a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,8 +18,8 @@ if(APPLE)
   set(OSX_SRCS "src/SDL12_compat_objc.m")
   set_source_files_properties(${OSX_SRCS} PROPERTIES LANGUAGE C)
   # the following matches SDL-1.2 Xcode project file
-  set(DYLIB_COMPAT_VERSION 1.0.0)
-  set(DYLIB_CURRENT_VERSION 12.50.0)
+  set(DYLIB_COMPAT_VERSION 1.0.0 CACHE STRING "library compatibility version")
+  set(DYLIB_CURRENT_VERSION 12.50.0 CACHE STRING "library current version")
   include_directories("/opt/X11/include")  # hack.
 endif()
 if(WIN32)