fuzz: minimum fuzzers environment lacks libcURL

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>