librt must be tested before creating Makefile
the bug has been introduced in r2817

auto/os/features

diff --git a/auto/os/features b/auto/os/features
index ae0590e..140e26b 100644
--- a/auto/os/features
+++ b/auto/os/features
@@ -252,3 +252,25 @@
         NGX_LIBDL="-ldl"
     fi
 fi
+
+
+ngx_feature="sched_yield()"
+ngx_feature_name="NGX_HAVE_SCHED_YIELD"
+ngx_feature_run=no
+ngx_feature_incs="#include <sched.h>"
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="sched_yield()"
+. auto/feature
+
+
+if [ $ngx_found != yes ]; then
+
+    ngx_feature="sched_yield() in librt"
+    ngx_feature_libs="-lrt"
+    . auto/feature
+
+    if [ $ngx_found = yes ]; then
+        CORE_LIBS="$CORE_LIBS -lrt"
+    fi
+fi

auto/unix

diff --git a/auto/unix b/auto/unix
index 399e54c..687a23a 100755
--- a/auto/unix
+++ b/auto/unix
@@ -163,28 +163,6 @@
 . auto/feature
 
 
-ngx_feature="sched_yield()"
-ngx_feature_name="NGX_HAVE_SCHED_YIELD"
-ngx_feature_run=no
-ngx_feature_incs="#include <sched.h>"
-ngx_feature_path=
-ngx_feature_libs=
-ngx_feature_test="sched_yield()"
-. auto/feature
-
-
-if [ $ngx_found != yes ]; then
-
-    ngx_feature="sched_yield() in librt"
-    ngx_feature_libs="-lrt"
-    . auto/feature
-
-    if [ $ngx_found = yes ]; then
-        CORE_LIBS="$CORE_LIBS -lrt"
-    fi
-fi
-
-
 ngx_feature="mmap(MAP_ANON|MAP_SHARED)"
 ngx_feature_name="NGX_HAVE_MAP_ANON"
 ngx_feature_run=yes