Always define something for required compiler extentions.  Silence
syntax errors that occur with TenDRA and GNUC's #warning.

Index: cdefs.h
===================================================================
RCS file: /work/repo/src/sys/sys/cdefs.h,v
retrieving revision 1.68
diff -u -r1.68 cdefs.h
--- cdefs.h	21 Oct 2002 20:50:30 -0000	1.68
+++ cdefs.h	5 Dec 2002 18:00:12 -0000
@@ -113,6 +113,11 @@
  * in a different (wrong) way).  If we do not provide an implementation
  * for a given compiler, let the compile fail if it is told to use
  * a feature that we cannot live without.
+ *
+ * XXX the check for lint here is incorrect, since either your lint supports
+ * GNUC or it doesn't.  Some kernel source code is very GNUC-centric, so we
+ * need this hack here until those GNUCisms are fixed.  In reality, having
+ * hacks like this usually extend the life of bugs.
  */
 #ifdef lint
 #define	__dead2
@@ -121,19 +126,10 @@
 #define	__packed
 #define	__aligned(x)
 #define	__section(x)
-#else
-#if __GNUC__ < 2 || __GNUC__ == 2 && __GNUC_MINOR__ < 5
-#define	__dead2
-#define	__pure2
-#define	__unused
-#endif
-#if __GNUC__ == 2 && __GNUC_MINOR__ >= 5 && __GNUC_MINOR__ < 7
+#elif __GNUC__ == 2 && __GNUC_MINOR__ >= 5 && __GNUC_MINOR__ < 7
 #define	__dead2		__attribute__((__noreturn__))
 #define	__pure2		__attribute__((__const__))
-#define	__unused
-/* XXX Find out what to do for __packed, __aligned and __section */
-#endif
-#if __GNUC__ == 2 && __GNUC_MINOR__ >= 7 || __GNUC__ == 3
+#elif __GNUC__ == 2 && __GNUC_MINOR__ >= 7 || __GNUC__ == 3
 #define	__dead2		__attribute__((__noreturn__))
 #define	__pure2		__attribute__((__const__))
 #define	__unused	__attribute__((__unused__))
@@ -141,6 +137,25 @@
 #define	__aligned(x)	__attribute__((__aligned__(x)))
 #define	__section(x)	__attribute__((__section__(x)))
 #endif
+
+/* Default to NOP for compiler-dependent extentions. */
+#ifndef __dead2
+#define	__dead2
+#endif
+#ifndef __pure2
+#define	__pure2
+#endif
+#ifndef __unused
+#define	__unused
+#endif
+#ifndef __packed
+#define	__packed
+#endif
+#ifndef __aligned
+#define	__aligned(x)
+#endif
+#ifndef __section
+#define	__section(x)
 #endif
 
 /* XXX: should use `#if __STDC_VERSION__ < 199901'. */
@@ -226,6 +241,14 @@
  * The alternative is: #define __IDSTRING(name,string)  [nothing]
  */
 #define	__IDSTRING(name,string)	static const char name[] __unused = string
+#endif
+
+/*
+ * TenDRA looks inside conditionals that don't apply (ie. #if __GNUC__).
+ * #warning is the most likely cause of syntax errors, so work around this.
+ */
+#ifdef __TenDRA__
+#pragma	TenDRA directive warning (ignore) allow
 #endif
 
 /*