Support clang compiler

Author: Ryzee119

src/common/tusb_compiler.h

@@ -123,11 +123,15 @@
 //--------------------------------------------------------------------+
 
 // TODO refactor since __attribute__ is supported across many compiler
-#if defined(__GNUC__)
+#if defined(__GNUC__) || defined (__clang__)
   #define TU_ATTR_ALIGNED(Bytes)        __attribute__ ((aligned(Bytes)))
   #define TU_ATTR_SECTION(sec_name)     __attribute__ ((section(#sec_name)))
   #define TU_ATTR_PACKED                __attribute__ ((packed))
-  #define TU_ATTR_WEAK                  __attribute__ ((weak))
+  #if defined(__clang__)
+    #define TU_ATTR_WEAK                  __attribute__ ((weak_import))
+  #else
+    #define TU_ATTR_WEAK                  __attribute__ ((weak))
+  #endif
   #ifndef TU_ATTR_ALWAYS_INLINE // allow to override for debug
     #define TU_ATTR_ALWAYS_INLINE       __attribute__ ((always_inline))
   #endif