Added API function to get CPU cache line size.

include/SDL_cpuinfo.h

@@ -51,6 +51,14 @@ extern "C" {
  */
 extern DECLSPEC int SDLCALL SDL_GetCPUCount(void);
 
+/**
+ *  This function returns the L1 cache line size of the CPU
+ *
+ *  This is useful for determining multi-threaded structure padding
+ *  or SIMD prefetch sizes.
+ */
+extern DECLSPEC int SDLCALL SDL_GetCPUCacheLineSize(void);
+
 /**
  *  This function returns true if the CPU has the RDTSC instruction.
  */