minizip: disable compatibility headers

minizip enables zip.h and unzip.h compatibility headers since version
2.7.2 and
https://github.com/nmoinvaz/minizip/commit/1b2b32c8b8c7ea441b14a2fd827d7e2dc886776c

This is an issue as php fails to build if minizip is built after libzip
because minizip installs a zip.h header without zip_stat, ZIP_CREATE,
ZIP_FL_NOCASE, zip_fopen, etc ...

So until the compatibility headers are enhanced/fixed in minizip, disable them

Fixes:
 - http://autobuild.buildroot.org/results/7b41f4e4a521b1e17aa885aac4419b26e0dd8700



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>