[PATCH] tools: Fix str_error_r() Werror=restrict build

[Sergey Senozhatsky]

Commit c8b5f2c96d1bf6c ("tools: Introduce str_error_r()") added
an str_error_r() wrapper which makes gcc8 unhappy due to
restrict-qualified parameter aliasing violation:

../lib/str_error_r.c: In function âstr_error_râ:
../lib/str_error_r.c:25:3: error: passing argument 1 to restrict-qualified parameter aliases with argument 5 [-Werror=restrict]
   snprintf(buf, buflen, "INTERNAL ERROR: strerror_r(%d, %p, %zd)=%d", errnum, buf, buflen, err);
   ^~~~~~~~
cc1: all warnings being treated as errors

Workaround that aliasing error by creating an additional stack
variable which holds the buf pointer value we passed to strerror_r().

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
 tools/lib/str_error_r.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/lib/str_error_r.c b/tools/lib/str_error_r.c
index d6d65537b0d9..11c3425f272b 100644
--- a/tools/lib/str_error_r.c
+++ b/tools/lib/str_error_r.c
@@ -21,7 +21,12 @@
 char *str_error_r(int errnum, char *buf, size_t buflen)
 {
 	int err = strerror_r(errnum, buf, buflen);
-	if (err)
-		snprintf(buf, buflen, "INTERNAL ERROR: strerror_r(%d, %p, %zd)=%d", errnum, buf, buflen, err);
+	if (err) {
+		char *err_buf = buf;
+
+		snprintf(err_buf, buflen,
+			 "INTERNAL ERROR: strerror_r(%d, %p, %zd)=%d",
+			 errnum, buf, buflen, err);
+	}
 	return buf;
 }
-- 
2.16.2