Support POSIX semaphores on Linux.
This configure test must run before auto/make, because it adds library.
auto/unix was placed after auto/make just for historical reasons.

Patch by Denis F. Latypoff
diff --git a/auto/configure b/auto/configure
index 8ee1c80..8ef3a9a 100755
--- a/auto/configure
+++ b/auto/configure
@@ -53,6 +53,7 @@
 if [ "$NGX_PLATFORM" != win32 ]; then
     . auto/os/features
     . auto/threads
+    . auto/unix
 fi
 
 . auto/modules
@@ -99,10 +100,6 @@
 . auto/lib/make
 . auto/install
 
-if [ "$NGX_PLATFORM" != win32 ]; then
-    . auto/unix
-fi
-
 # STUB
 . auto/stubs