Ensure that recursive QMAKE_EXTRA_TARGETS use the correct makefile

Ensure that recursive QMAKE_EXTRA_TARGETS use the correct makefile

Recursive QMAKE_EXTRA_TARGETS were omitting the `-f' option to make.
This would break in the case where the correct makefile was not named
`Makefile'.  The included autotest demonstrates the problem.

Note that this was fixed for normal targets back in 2005
by faac7bd178654fd67a6f3f9cf4f6f2605071448d (p4 202370), but was not
fixed for extra targets.

Reviewed-by: ossi