a2753de contains some regressions, causing `fixupobj` to be
inappropriately suppressed when `-MD` or `-MMD` is passed.
This commit reverts most changes by a2753de, and:
- Treats all invocations of the compiler with `-M` and `-MM` as with the
`cpp` intent, since these flags imply `-E`.
- Handle the dependency output path specified by `-MF`.
+ This is trivial for `cosmocross` since the script does not throw
objects to and from temporary directories.
+ For `cosmocc`, the file names are calculated based on the `-MF`
value provided by the user. If this flag is not specified, the script
generates the file name based on the output file using GCC rules.
Then, before calling the real compilers, an additional `-MF` flag is
passed to override the dependency outputs with mangled file names.
83a8686c06