tests/make: demonstrate unhelpful debug log in case of errors

The releng build job that runs lint fails.  It outputs the usage message
of lint, which doesn't include the failing option.  After that, make
outputs:

*** Failed target: lint-cgdconfig
*** Failed commands:
${LINT} ${LINTFLAGS} \
    ${_LDFLAGS.${:Ucgdconfig}:C/-L[  ]*/-L/Wg:M-L*} \
    ${LOBJS.${:Ucgdconfig}} ${_LDADD.${:Ucgdconfig}}

Make doesn't output the expanded command, therefore the log doesn't show
the offending option '-pthread' that leads to the usage message.

(rillig)