Create sub-directory for fuzzers under nativetest.

This CL changes BUILD_FUZZ_TEST to generate binaries in a
sub-directory called fuzzers/ under the nativetest directory. This
allows fuzzers to be distinguished from the other native tests and
makes it easier to perform automated fuzz-testing.

Bug: 25714111
Change-Id: I452e43f15728ec9168dd44776b6ffcea6037fa7f
1 file changed