CLEANUP: pools: factor all malloc_trim() calls into trim_all_pools()

The code was slightly cleaned up by removing repeated occurrences of ifdefs
and moving that into a single trim_all_pools() function.
diff --git a/src/pool.c b/src/pool.c
index d9d8095..60f21d6 100644
--- a/src/pool.c
+++ b/src/pool.c
@@ -40,6 +40,21 @@
 static int mem_fail_rate = 0;
 #endif
 
+#if defined(HA_HAVE_MALLOC_TRIM)
+/* ask the allocator to trim memory pools */
+static void trim_all_pools(void)
+{
+	if (using_libc_allocator)
+		malloc_trim(0);
+}
+
+#else
+
+static void trim_all_pools(void)
+{
+}
+#endif
+
 /* Try to find an existing shared pool with the same characteristics and
  * returns it, otherwise creates this one. NULL is returned if no memory
  * is available for a new creation. Two flags are supported :
@@ -275,9 +290,7 @@
 /* This function might ask the malloc library to trim its buffers. */
 void pool_gc(struct pool_head *pool_ctx)
 {
-#if defined(HA_HAVE_MALLOC_TRIM)
-	malloc_trim(0);
-#endif
+	trim_all_pools();
 }
 
 #else /* CONFIG_HAP_NO_GLOBAL_POOLS */
@@ -339,9 +352,7 @@
 		}
 	}
 
-#if defined(HA_HAVE_MALLOC_TRIM)
-	malloc_trim(0);
-#endif
+	trim_all_pools();
 
 	if (!isolated)
 		thread_release();
@@ -358,9 +369,7 @@
 /* This function might ask the malloc library to trim its buffers. */
 void pool_gc(struct pool_head *pool_ctx)
 {
-#if defined(HA_HAVE_MALLOC_TRIM)
-	malloc_trim(0);
-#endif
+	trim_all_pools();
 }
 
 #endif /* CONFIG_HAP_POOLS */