apache: add compile fix for libxml-2.12.x

libxml2 restructured includes, thus another include is now required
otherwise build fails.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

net/apache/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=apache
 PKG_VERSION:=2.4.57
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 PKG_SOURCE_NAME:=httpd
 
 PKG_SOURCE:=$(PKG_SOURCE_NAME)-$(PKG_VERSION).tar.bz2

net/apache/patches/100_compile-fix-libxml2-2.12.x.patch

@@ -0,0 +1,10 @@
+--- a/modules/filters/mod_xml2enc.c
++++ b/modules/filters/mod_xml2enc.c
+@@ -35,6 +35,7 @@
+ #endif
+ 
+ /* libxml2 */
++#include <libxml/xmlstring.h>
+ #include <libxml/encoding.h>
+ 
+ #if defined(__clang__)