fix 'ignoring return value' compiler warnings

Various system functions like write() are marked with the
__warn_unused_result__ attribute, which causes an 'ignoring return value'
warning to be emitted, even if the function call result is cast to (void).

The generic solution seems to be

    int rc = write(...);
    PERL_UNUSED_VAR(rc);

1 files changed, 3 insertions, 1 deletions

diff --git a/thread.h b/thread.h
index de23d75559..cd5563511d 100644
--- a/thread.h
+++ b/thread.h
@@ -336,7 +336,9 @@
 #  define ALLOC_THREAD_KEY \
     STMT_START {						\
 	if (pthread_key_create(&PL_thr_key, 0)) {		\
-            (void)write(2, STR_WITH_LEN("panic: pthread_key_create failed\n")); \
+            int rc;                                             \
+            rc = write(2, STR_WITH_LEN("panic: pthread_key_create failed\n")); \
+            PERL_UNUSED_VAR(rc);                                \
 	    exit(1);						\
 	}							\
     } STMT_END