tls: removed inline specifier and renamed safe_shm_available()

- became shm_available_safe() to have the shm_ prefix which common for
  shm functions
- declaring inline in c header file and implementing in c source file
  makes clang throw compile warnings

mem/shm_mem.c

@@ -254,7 +254,7 @@ void shm_mem_destroy(void)
 #endif
 }
 
-inline unsigned long safe_shm_available()
+unsigned long shm_available_safe()
 {
 	unsigned long ret;
 	shm_lock();

mem/shm_mem.h

@@ -314,7 +314,7 @@ do{\
 
 /* multi-process safe version of shm_available()
  */
-inline unsigned long safe_shm_available();
+unsigned long shm_available_safe();
 
 
 #endif /* shm_mem_h */