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

Index: qemu-0.12.4/configure
===================================================================
--- qemu-0.12.4.orig/configure
+++ qemu-0.12.4/configure
@@ -99,6 +99,7 @@ QEMU_CFLAGS="-Wstrict-prototypes -Wredun
 QEMU_CFLAGS="-D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE $QEMU_CFLAGS"
 QEMU_CFLAGS="-U_FORTIFY_SOURCE $QEMU_CFLAGS"
 QEMU_CFLAGS="-I. -I\$(SRC_PATH) $QEMU_CFLAGS"
+QEMU_CFLAGS="$QEMU_CFLAGS $CFLAGS"
 LDFLAGS="-g $LDFLAGS"
 
 gcc_flags="-Wold-style-declaration -Wold-style-definition"