Improved fix for __always_inline redefinition bug

Instead of changing based on the version of GCC, check for the presence of the macro instead.

tmk_core/protocol/arm_atsam/usb/compiler.h

@@ -134,13 +134,15 @@
  * heuristics and inline the function no matter how big it thinks it
  * becomes.
  */
+#if !defined(__always_inline)
 #if defined(__CC_ARM)
 #  define __always_inline             __forceinline
-#elif (defined __GNUC__ && __GNUC__ <= 6)
+#elif (defined __GNUC__)
 #  define __always_inline             __attribute__((__always_inline__))
 #elif (defined __ICCARM__)
 #  define __always_inline             _Pragma("inline=forced")
 #endif
+#endif
 
 /**
  * \def __no_inline