unix: replace use of strcpy in mkerrors.sh

On OpenBSD-current, clang emits a warning message to standard output for the use of strcpy, e.g.:

_errors.c(/tmp/_errors-673190.o:(main)): warning: strcpy() is almost always misused, please use strlcpy()

This message makes it into the Go source being created, causing gofmt to error on the invalid syntax, and leaving the zerrors file empty.

Using strlcpy would be preferred here, but strncpy is enough to silence this message, and is more portable.

Change-Id: I16404d74c4406dadda87f211fc0ba062de0d11ac
GitHub-Last-Rev: a43b6fb
GitHub-Pull-Request: #147
Reviewed-on: https://go-review.googlesource.com/c/sys/+/468399
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>

unix/mkerrors.sh

@@ -741,7 +741,8 @@ main(void)
 		e = errors[i].num;
 		if(i > 0 && errors[i-1].num == e)
 			continue;
-		strcpy(buf, strerror(e));
+		strncpy(buf, strerror(e), sizeof(buf) - 1);
+		buf[sizeof(buf) - 1] = '\0';
 		// lowercase first letter: Bad -> bad, but STREAM -> STREAM.
 		if(A <= buf[0] && buf[0] <= Z && a <= buf[1] && buf[1] <= z)
 			buf[0] += a - A;
@@ -760,7 +761,8 @@ main(void)
 		e = signals[i].num;
 		if(i > 0 && signals[i-1].num == e)
 			continue;
-		strcpy(buf, strsignal(e));
+		strncpy(buf, strsignal(e), sizeof(buf) - 1);
+		buf[sizeof(buf) - 1] = '\0';
 		// lowercase first letter: Bad -> bad, but STREAM -> STREAM.
 		if(A <= buf[0] && buf[0] <= Z && a <= buf[1] && buf[1] <= z)
 			buf[0] += a - A;