Remove unused HIDDEN_DECL macro

CMakeLists.txt

@@ -359,7 +359,6 @@ int main()
 ENDIF()
 
 # Set visibility/export options if available
-SET(HIDDEN_DECL "")
 IF(WIN32)
     SET(EXPORT_DECL "__declspec(dllexport)")
     IF(NOT MINGW)
@@ -388,7 +387,6 @@ ELSE()
         CHECK_C_COMPILER_FLAG(-fvisibility=hidden HAVE_VISIBILITY_HIDDEN_SWITCH)
         IF(HAVE_VISIBILITY_HIDDEN_SWITCH)
             SET(EXTRA_CFLAGS "${EXTRA_CFLAGS} -fvisibility=hidden")
-            SET(HIDDEN_DECL "__attribute__((visibility(\"hidden\")))")
         ENDIF()
     ENDIF()
 

config.h.in

@@ -8,9 +8,6 @@
 /* Define a built-in call indicating an aligned data pointer */
 #define ASSUME_ALIGNED(x, y) ${ASSUME_ALIGNED_DECL}
 
-/* Explicit hidden visibility attribute */
-#define HIDDEN_DECL ${HIDDEN_DECL}
-
 /* Define if HRTF data is embedded in the library */
 #cmakedefine ALSOFT_EMBED_HRTF_DATA