- make #error fail the compilation (i.e. non zero exit status)
- add #warning which is non fatal.

#warning is not part of ANSI but seems to be widely supported, and cpp's continual
grumbling gets on my nerves.

Reference: /n/sources/patch/applied/cpp-warning
Date: Thu Dec 18 17:05:21 CET 2008
Signed-off-by: steve@quintile.net

--- /sys/src/cmd/cpp/nlist.c	Thu Dec 18 17:02:45 2008
+++ /sys/src/cmd/cpp/nlist.c	Thu Dec 18 17:02:42 2008
@@ -33,6 +33,7 @@
 	"undef",	KUNDEF,		ISKW,
 	"line",		KLINE,		ISKW,
 	"error",	KERROR,		ISKW,
+	"warning",	KWARNING,	ISKW,		// extension to ANSI
 	"pragma",	KPRAGMA,	ISKW,
 	"eval",		KEVAL,		ISKW,
 	"defined",	KDEFINED,	ISDEFINED+ISUNCHANGE,
--- /sys/src/cmd/cpp/cpp.h	Thu Dec 18 17:02:50 2008
+++ /sys/src/cmd/cpp/cpp.h	Thu Dec 18 17:02:47 2008
@@ -20,7 +20,7 @@
 		DSHARP1, NAME1, DEFINED, UMINUS };
 
 enum kwtype { KIF, KIFDEF, KIFNDEF, KELIF, KELSE, KENDIF, KINCLUDE, KDEFINE,
-		KUNDEF, KLINE, KERROR, KPRAGMA, KDEFINED,
+		KUNDEF, KLINE, KERROR, KWARNING, KPRAGMA, KDEFINED,
 		KLINENO, KFILE, KDATE, KTIME, KSTDC, KEVAL };
 
 #define	ISDEFINED	01	/* has #defined value */
--- /sys/src/cmd/cpp/cpp.c	Thu Dec 18 17:02:54 2008
+++ /sys/src/cmd/cpp/cpp.c	Thu Dec 18 17:02:52 2008
@@ -208,7 +208,12 @@
 
 	case KERROR:
 		trp->tp = tp+1;
-		error(WARNING, "#error directive: %r", trp);
+		error(ERROR, "#error directive: %r", trp);
+		break;
+
+	case KWARNING:
+		trp->tp = tp+1;
+		error(WARNING, "#warning directive: %r", trp);
 		break;
 
 	case KLINE: