[committed][gdb/testsuite] Fix Wunused-result warning in until-reverse.c

[Tom de Vries <tdevries@suse.de>]

Hi,

When running test-case gdb.reverse/until-reverse.exp or
gdb.reverse/until-precsave.exp with gcc-10, we run into a Wunused-result
warning:
...
gdb compile failed, gdb.reverse/until-reverse.c: In function 'main':
gdb.reverse/until-reverse.c:40:14: warning: ignoring return value of \
  'malloc' declared with attribute 'warn_unused_result' [-Wunused-result]
   40 |       (void) malloc (1);
      |              ^~~~~~~~~~
...

Fix this by using the result of malloc as argument to a free call.

Tested on x86_64-linux.

Committed to trunk.

Thanks,
- Tom

[gdb/testsuite] Fix Wunused-result warning in until-reverse.c

gdb/testsuite/ChangeLog:

2020-05-01  Tom de Vries  <tdevries@suse.de>

	* gdb.reverse/until-reverse.c (main): Fix Wunused-result warning.

---
 gdb/testsuite/gdb.reverse/until-reverse.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.reverse/until-reverse.c b/gdb/testsuite/gdb.reverse/until-reverse.c
index e523235f34c..a8d8aed9aac 100644
--- a/gdb/testsuite/gdb.reverse/until-reverse.c
+++ b/gdb/testsuite/gdb.reverse/until-reverse.c
@@ -37,7 +37,8 @@ main (int argc, char **argv, char **envp)
     {
       /* We're used by a test that requires malloc, so make sure it is
 	 in the executable.  */
-      (void) malloc (1);
+      void *p = malloc (1);
+      free (p);
       return 1;
     }