In native builds, qemu can fail to find zlib development files in the native 
sysroot and the build machine might not have zlib-dev packages installed.

Add CFLAGS to qemu's CFLAGS which in the native case means BUILD_CFLAGS are
added and files in the sysroot can be found.

Patch from Paul Eggleton, Comments by RP 28/11/10

Upstream-Status: Inappropriate [embedded specific]

Index: qemu-1.4.0/configure
===================================================================
--- qemu-1.4.0.orig/configure	2013-02-15 15:05:35.000000000 -0800
+++ qemu-1.4.0/configure	2013-02-25 13:44:17.915273181 -0800
@@ -286,6 +286,7 @@
 QEMU_CFLAGS="-Wstrict-prototypes -Wredundant-decls $QEMU_CFLAGS"
 QEMU_CFLAGS="-D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE $QEMU_CFLAGS"
 QEMU_INCLUDES="-I. -I\$(SRC_PATH) -I\$(SRC_PATH)/include"
+QEMU_CFLAGS="$QEMU_CFLAGS $CFLAGS"
 if test "$debug_info" = "yes"; then
     CFLAGS="-g $CFLAGS"
     LDFLAGS="-g $LDFLAGS"