If using GNUC and ELF, make __IDSTRING() expand into an inline asm

statement to put the rcsid into the .comment section.  This allows
the comments (ie:version id's of compiler, headers, source, etc) to be
stripped out with the standard tools (strip/objcopy).  SVR4 has a
tool called 'mcs' (manipulate comment section) which allows you to
add/remove/compact strings.  Removing duplicate strings helps a lot
if the headers generate them.
Using __attribute__((section(".comment"))) would probably also work,
but that still leaves the RCSID occupying C name space somewhere.

sys/sys/cdefs.h

@@ -190,7 +190,11 @@
 #endif	/* __ELF__ */
 #endif	/* __GNUC__ */
 
+#if defined(__GNUC__) && defined(__ELF__)
+#define	__IDSTRING(name,string)	__asm__(".ident\t\"" string "\"")
+#else
 #define	__IDSTRING(name,string)	static const char name[] __unused = string
+#endif
 
 #ifndef	__RCSID
 #define	__RCSID(s)	__IDSTRING(rcsid,s)