Diagnostic Biobuf was initialised too late to catch
output file creat [sic] errors.

Added a %r to give the OS's reason, nice on plan9 but
perhaps too much of a portability hit for some.

-Steve

Reference: /n/sources/patch/applied/8c-op-file-error
Date: Thu Sep  7 15:30:31 CES 2006
Signed-off-by: steve@quintile.net

--- /sys/src/cmd/cc/lex.c	Thu Sep  7 15:28:38 2006
+++ /sys/src/cmd/cc/lex.c	Thu Sep  7 15:28:26 2006
@@ -157,6 +157,7 @@
 			include[0] = strdup(ofile);
 	} else
 		p = ofile;
+
 	if(outfile == 0) {
 		outfile = p;
 		if(outfile) {
@@ -186,6 +187,7 @@
 			setinclude("/sys/include");
 		}
 	}
+	Binit(&diagbuf, 1, OWRITE);
 	if((debug['a'] || debug['Z']) && !debug['n']) {
 		outfile = 0;
 		Binit(&outbuf, dup(1, -1), OWRITE);
@@ -193,13 +195,12 @@
 	} else {
 		c = mycreat(outfile, 0664);
 		if(c < 0) {
-			diag(Z, "cannot open %s", outfile);
+			diag(Z, "cannot open %s - %r", outfile);
 			outfile = 0;
 			errorexit();
 		}
 		Binit(&outbuf, c, OWRITE);
 	}
-	Binit(&diagbuf, 1, OWRITE);
 	newio();
 
 	/* Use an ANSI preprocessor */