Configure: fix tests with multi-level relative build directory.

Based on a patch by Piotr Sikora.

auto/unix

diff --git a/auto/unix b/auto/unix
index 595f905..b7b7a25 100755
--- a/auto/unix
+++ b/auto/unix
@@ -505,14 +505,7 @@
 
 # POSIX types
 
-case "$NGX_AUTO_CONFIG_H" in
-    /*)
-        NGX_INCLUDE_AUTO_CONFIG_H="#include \"$NGX_AUTO_CONFIG_H\""
-    ;;
-    *)
-        NGX_INCLUDE_AUTO_CONFIG_H="#include \"../$NGX_AUTO_CONFIG_H\""
-    ;;
-esac
+NGX_INCLUDE_AUTO_CONFIG_H="#include \"ngx_auto_config.h\""
 
 ngx_type="uint64_t"; ngx_types="u_int64_t"; . auto/types/typedef