cpuinfo: first attempt at SDL_HasNEON() implementation.

include/SDL_config.h.cmake

@@ -171,6 +171,8 @@
 #cmakedefine HAVE_PTHREAD_SETNAME_NP 1
 #cmakedefine HAVE_PTHREAD_SET_NAME_NP 1
 #cmakedefine HAVE_SEM_TIMEDWAIT 1
+#cmakedefine HAVE_GETAUXVAL 1
+
 #elif __WIN32__
 #cmakedefine HAVE_STDARG_H 1
 #cmakedefine HAVE_STDDEF_H 1

include/SDL_config.h.in

@@ -173,6 +173,7 @@
 #undef HAVE_PTHREAD_SETNAME_NP
 #undef HAVE_PTHREAD_SET_NAME_NP
 #undef HAVE_SEM_TIMEDWAIT
+#undef HAVE_GETAUXVAL
 
 #else
 #define HAVE_STDARG_H   1

include/SDL_cpuinfo.h

@@ -144,6 +144,11 @@ extern DECLSPEC SDL_bool SDLCALL SDL_HasAVX(void);
  */
 extern DECLSPEC SDL_bool SDLCALL SDL_HasAVX2(void);
 
+/**
+ *  This function returns true if the CPU has NEON (ARM SIMD) features.
+ */
+extern DECLSPEC SDL_bool SDLCALL SDL_HasNEON(void);
+
 /**
  *  This function returns the amount of RAM configured in the system, in MB.
  */