Discard always_inline if __NO_INLINE__ is defined

Workaround a compiler bug in (at least) GCC 4.2.1 if always_inline is
used with forward declarations and optimizations are disabled.

Author: k0ekk0ek

src/attributes.h

@@ -23,7 +23,12 @@
 # define unlikely(params) (params)
 
 #else // _MSC_VER
-# if zone_has_attribute(always_inline) || zone_has_gnuc(3, 1)
+# if (zone_has_attribute(always_inline) || zone_has_gnuc(3, 1)) && ! defined __NO_INLINE__
+    // Compilation using GCC 4.2.1 without optimizations fails.
+    //   sorry, unimplemented: inlining failed in call to ...
+    // GCC 4.1.2 and GCC 4.30 compile forward declared functions annotated
+    // with __attribute__((always_inline)) without problems. Test if
+    // __NO_INLINE__ is defined and define macro accordingly.
 #   define really_inline inline __attribute__((always_inline))
 # else
 #   define really_inline inline