Set `+incdir` for every primary source directory.  Previously, only the
root primary source directory would be set.

This change is done to allow for the FIRRTL ABI related to bind layers to
be changed to _not_ use an FIRRTL compiler output directory-relative path
for `` `include `` [[1]].  This is necessary because some flows are
rearranging the directory structure of Chisel-generated Verilog, which
includes layers, and paths relative to the root will break.

This is a compromise between complexity of the build system, ABI
simplicitly, and ease of directory manipulation.  This has the effect of
users with custom build flows will need to recognize that they need to set
the `+incdir` recursively based on all output directories that were
created.  Practically, this is easy to do.

[1]: llvm/circt#8474

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

Set `+incdir` for every primary source directory.  Previously, only the
root primary source directory would be set.

This change is done to allow for the FIRRTL ABI related to bind layers to
be changed to _not_ use an FIRRTL compiler output directory-relative path
for `` `include `` [[1]].  This is necessary because some flows are
rearranging the directory structure of Chisel-generated Verilog, which
includes layers, and paths relative to the root will break.

This is a compromise between complexity of the build system, ABI
simplicitly, and ease of directory manipulation.  This has the effect of
users with custom build flows will need to recognize that they need to set
the `+incdir` recursively based on all output directories that were
created.  Practically, this is easy to do.

[1]: llvm/circt#8474

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

ref: llvm/circt#8474

Signed-off-by: unlsycn <unlsycn@unlsycn.com>

ref: llvm/circt#8474

Signed-off-by: unlsycn <unlsycn@unlsycn.com>

ref: llvm/circt#8474

Signed-off-by: unlsycn <unlsycn@unlsycn.com>

ref: llvm/circt#8474

Signed-off-by: unlsycn <unlsycn@unlsycn.com>

This reverts a suggestion [[1]] I made on llvm#8458.  This changes
the (undocumented) ABI of FIRRTL layers to _not_ include any directory
information in the `` `include `` directives used to enable layers.  The
reason for this is that using the full paths (relative to the root output
directory) prevents rearranaging directories after compilation.

The downside to this is that users must include more `+incdir` command
line options to include _all_ directories in a design.  However, I think
this is reasonable.

I do think that we can roll this back to use the original behavior in the
future in a backwards-compatible way.  I.e., making the change from not
including the full path to including the full path won't break any
downstream tools as these will just be including _too many_ `+incdir`s.

[1]: llvm#8458 (review)

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>