fuzz: avoid building t/fuzz/parse_ini by default

fuzz: avoid building t/fuzz/parse_ini by default

With a vanilla build t/fuzz/parse_ini will segfault because the symbol
FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION is not defined. If the symbol
FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION is defined, fio won't tear down
shared memory on program termination. Not tearing down shared memory is
necessary for t/fuzz/parse_ini to work correctly.

Don't build t/fuzz/parse_ini unless CFLAGS contains
-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>