fuzz: minimum fuzzers environment lacks libcURL

The "fuzz smoke test" job compiles various .o files to create libgit.a and others, but the final build product of the fuzzer build is *not* "git". Since the job is not interested in building a working "git", it does not define any build flags, and among the notable ones that are missing is NO_CURL---even though the CI environment that runs the job does not have libcURL development package installed. This obviously leads to a build failure. Pass NO_CURL=NoThanks to "make" to make sure things will build correctly, if we add any conditional compilation with "#ifdef NO_CURL ... #endif" in the codebase. Signed-off-by: Junio C Hamano <gitster@pobox.com>