Bug report

Inconfigure.ac we have several fallbacks when pkg-config is missing or a package does not provide a.pc file. The fallbacks do not take custom cflags into account. For example the block forzlib doesAC_CHECK_HEADERS([zlib.h]) andAC_CHECK_LIB([z]) without settingCFLAGS="$CFLAGS $ZLIB_CFLAGS" first.