fuzz: Create fuzzers with default and custom crypto plugins

The pa_tnc fuzzer does not rely on any plugins and the pb_tnc fuzzer is
a bit special in that it does use code from the tnccs-20 plugin, but that
doesn't actually have to be loaded as such. The fuzzer directly calls
statically linked code from the plugin.

scripts/test.sh

@@ -433,6 +433,8 @@ fuzzing)
 	CFLAGS="$CFLAGS -DNO_CHECK_MEMWIPE"
 	CONFIG="--enable-fuzzing --enable-static --disable-shared --disable-scripts
 			--enable-imc-test --enable-tnccs-20 --enable-eap-radius"
+	# enable the custom crypto plugins
+	CONFIG="$CONFIG --enable-sha1 --enable-sha2 --enable-sha3 --enable-mgf1 --enable-gmp"
 	# don't run any of the unit tests
 	export TESTS_RUNNERS=
 	# prepare corpora