[flang][driver] Add pre-processing type for Fortran pre-processed files (#104664)

When using `--save-temps`, flang-new emits (among other things) an
`<input>.i` file. These `.i` files are pre-processed Fortran files
containing information about the modules referenced by the input source
(these files are emitted by: `Parsing::EmitPreprocessedSource`).

This diff allows `.i` files emitted by flang-new to be treated as valid
files in the pre-processing phase. This, in turn, allows flang-new to
add pre-processing options (e.g. `-I`) when launching compilation jobs
for these files.

This solves a bug when using `--save-temps` with source files that
include modules from non-standard directories, for example:
```
flang-new -c --save-temps -I/tmp/module_dir -fno-integrated-as \
  /tmp/ModuleUser.f90
```
The problem was that `.i` files were treated as "binary" files and
therefore the return value for `types::getPreprocessedType(InputType)`
in `Flang::ConstructJob(...)` was `types::TY_INVALID`.

0 files changed, 0 insertions, 0 deletions