LP:781085 - MWL89 tree uses system zlib.h (instead of built in)

If remove developer zlib library from the system (apt-get remove zlib1g-dev for ubuntu) we get following error (5.3 compiles without a problem):

make[2]: Entering directory `/home/bell/maria/bzr/work-maria-5.3-mwl89-test/client'
gcc -DMYSQL_CLIENT_NO_THREADS -DDEFAULT_MYSQL_HOME='"/usr/local/mysql"' -DMYSQL_DATADIR='"/usr/local/mysql/var"' -I. -I../include -I../include -I../include -I../regex -Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror -DFORCE_INIT_OF_VARS -Wdeclaration-after-statement -g -Wall -Wextra -Wunused -Wwrite-strings -Wno-uninitialized -mtune=native -DUNIV_MUST_NOT_INLINE -DEXTRA_DEBUG -DSAFEMALLOC -DPEDANTIC_SAFEMALLOC -O0 -g3 -gdwarf-2 -DFORCE_INIT_OF_VARS -Wuninitialized -DUNIV_LINUX -MT checksum.o -MD -MP -MF .deps/checksum.Tpo -c -o checksum.o `test -f '../mysys/checksum.c' || echo './'`../mysys/checksum.c
../mysys/checksum.c:19:18: fatal error: zlib.h: No such file or directory
compilation terminated.
make[2]: *** [checksum.o] Error 1