Makefile: Let "make check-help" work without running ./configure

Makefile: Let "make check-help" work without running ./configure

Currently if you do "make check-help" in a fresh checkout, only an error
is printed which is not nice:

    $ make check-help V=1
    cc -nostdlib  -o check-help.mo
    cc: fatal error: no input files
    compilation terminated.
    rules.mak:115: recipe for target 'check-help.mo' failed
    make: *** [check-help.mo] Error 1

Move the config-host.mak condition into the body of
tests/Makefile.include and always include the rule for check-help.

Reported-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Fam Zheng <[email protected]>
Message-Id: <20170810085025[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Tested-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Fam Zheng <[email protected]>