Added (void) as we intentionally ignore returned values.

Requested by Igor Sysoev.

src/core/ngx_shmtx.c

diff --git a/src/core/ngx_shmtx.c b/src/core/ngx_shmtx.c
index 3414868..8a3178e 100644
--- a/src/core/ngx_shmtx.c
+++ b/src/core/ngx_shmtx.c
@@ -97,7 +97,7 @@
 #if (NGX_HAVE_POSIX_SEM)
 
         if (mtx->semaphore) {
-            ngx_atomic_fetch_add(mtx->wait, 1);
+            (void) ngx_atomic_fetch_add(mtx->wait, 1);
 
             if (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid)) {
                 return;

src/os/unix/ngx_process.c

diff --git a/src/os/unix/ngx_process.c b/src/os/unix/ngx_process.c
index 9f1936b..3eba6ce 100644
--- a/src/os/unix/ngx_process.c
+++ b/src/os/unix/ngx_process.c
@@ -555,7 +555,7 @@
      */
 
     if (ngx_accept_mutex_ptr) {
-        ngx_shmtx_force_unlock(&ngx_accept_mutex, pid);
+        (void) ngx_shmtx_force_unlock(&ngx_accept_mutex, pid);
     }
 
     /*