Add the showcheck target to the Makefile.

Makes it possible to see the varnishtest command invoked by check,
so as to use it to test individual vtc's.

src/Makefile.am

@@ -31,6 +31,11 @@ TEST_EXTENSIONS = .vtc
 VTC_LOG_COMPILER = varnishtest -v
 AM_VTC_LOG_FLAGS = -Dvmod_dispatch="$(VMOD_DISPATCH)"
 
+# echos the varnishtest command invoked by make check, for use with
+# indivdual vtc tests.
+showcheck:
+	@echo $(AM_TESTS_ENVIRONMENT) $(VTC_LOG_COMPILER) $(AM_VTC_LOG_FLAGS)
+
 TESTS = @VMOD_TESTS@
 
 EXTRA_DIST = \