fix error when cross-compiling with --system-zlib

This is broken since 1f461ac45b, where
Z_PREFIX was defined to namespace the bundled zlib symbols. The
bundled zlib is used by bootstrap.pro when cross-compiling which uses
the namespaced symbols. This breaks linking of rcc when --system-zlib
is used, as it will try to link to compress2 instead of z_compress2.

To fix this, the aliases are pulled in via zconf.h and the bundled
zlib is prepended to the INCLUDEPATH (i.e. before the system zlib).

Change-Id: Iec76cbdead40f888e2ac6a887ec8f3b7bc7db501
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/3rdparty/zlib.pri

@@ -1,5 +1,5 @@
 wince*: DEFINES += NO_ERRNO_H
-INCLUDEPATH += $$PWD/zlib
+INCLUDEPATH = $$PWD/zlib $$INCLUDEPATH
 SOURCES+= \
     $$PWD/zlib/adler32.c \
     $$PWD/zlib/compress.c \

src/corelib/tools/qbytearray.cpp

@@ -43,6 +43,7 @@
 #include <qmath.h>
 
 #ifndef QT_NO_COMPRESS
+#include <zconf.h>
 #include <zlib.h>
 #endif
 #include <ctype.h>