PHP: fixed incorrect time in interpreter error log messages.

Previously, the log message callback used a generic log function, that relied on the process time cache.
Since there were no time update calls in the application processes, all log lines were printed with the
same time, usually correlated with the process start.

Now, a non-cached logging function from libunit is used.

src/nxt_php_sapi.c

@@ -251,7 +251,7 @@ NXT_EXPORT nxt_app_module_t  nxt_app_module = {
 static nxt_php_target_t  *nxt_php_targets;
 static nxt_int_t         nxt_php_last_target = -1;
 
-static nxt_task_t  *nxt_php_task;
+static nxt_unit_ctx_t    *nxt_php_unit_ctx;
 #if defined(ZTS) && PHP_VERSION_ID < 70400
 static void              ***tsrm_ls;
 #endif
@@ -277,8 +277,6 @@ nxt_php_start(nxt_task_t *task, nxt_process_data_t *data)
     static nxt_str_t  user_str = nxt_string("user");
     static nxt_str_t  admin_str = nxt_string("admin");
 
-    nxt_php_task = task;
-
     conf = data->app;
     c = &conf->u.php;
 
@@ -405,6 +403,8 @@ nxt_php_start(nxt_task_t *task, nxt_process_data_t *data)
         return NXT_ERROR;
     }
 
+    nxt_php_unit_ctx = unit_ctx;
+
     nxt_unit_run(unit_ctx);
 
     nxt_unit_done(unit_ctx);
@@ -1277,5 +1277,6 @@ static void
 nxt_php_log_message(char *message TSRMLS_DC)
 #endif
 {
-    nxt_log(nxt_php_task, NXT_LOG_NOTICE, "php message: %s", message);
+    nxt_unit_log(nxt_php_unit_ctx, NXT_UNIT_LOG_NOTICE,
+                 "php message: %s", message);
 }