[PATCH] Correct reference to GCC compiler macro

[Joel Cunningham]

# HG changeset patch
# User Joel Cunningham <joel.cunningham at me.com>
# Date 1456860378 21600
#      Tue Mar 01 13:26:18 2016 -0600
# Node ID cce5f2f6ed76ffa0f6890e90e7b1b68718ffa8a9
# Parent  3b9fe734a76ca0863ec87596369690831e9f4086
Correct reference to GCC compiler macro

This commit corrects a small typo where __GNU__ was used in place of
__GNUC__

This was identified on a GCC system that built with undefined macros
treated as errors when used with #if

diff -r 3b9fe734a76c -r cce5f2f6ed76 src/core/ngx_config.h
--- a/src/core/ngx_config.h    Tue Mar 01 15:18:07 2016 +0300
+++ b/src/core/ngx_config.h    Tue Mar 01 13:26:18 2016 -0600
@@ -125,7 +125,7 @@
 #endif
 
 
-#if ((__GNU__ == 2) && (__GNUC_MINOR__ < 8))
+#if ((__GNUC__ == 2) && (__GNUC_MINOR__ < 8))
 #define NGX_MAX_UINT32_VALUE  (uint32_t) 0xffffffffLL
 #else
 #define NGX_MAX_UINT32_VALUE  (uint32_t) 0xffffffff