Revert "Only pass implicit -MQ to preprocessor if needed"

Revert "Only pass implicit -MQ to preprocessor if needed"

This reverts commit 19c3729d30640fc2c78242cb46136e619fdbd802 and also
removes the incorrect and superfluous condition that the fix fixes.

The reason for reverting is that the change introduced a nasty bug: the
dependency file will get an incorrect object file location if 1) build
directory != source directory and 2) -MF is not specified explictly by
the user.

Details: The dependency file is created by the preprocessor pass which
does not have access to the final output file name, so the preprocessor
uses the default object location derived from the source file location
instead.

Note that this partly reverts a compatibility improvement for EDG-based
compilers (see issue #460).

It should be possible to pass the dependency arguments to the compiler
instead of the preprocessor to make -MD/-MMD without -MQ work, but
that’s too risky to be done as a bug fix.

Fixes #499.