Add Forth script capability and fix compilation of loader install command

[stevek]

Summary

Add support for LOADER_RC setting in the pkgfs manifest (defaults to /loader.rc) to specify a Forth file to read from the pkgfs tarball and process by Ficl.
This allows for the tarball to do runtime things like load a platform-specific FDT blob, among other things.
The file_loadraw function grew an argument, but sys/boot/common/install.c did not get updated.

Test Plan

Used by Juniper Networks for network install images on non-x86 platforms.

[imp]

Looks good to me, but maybe you'd do the file_loadraw() one first...

[stevek]

In D8494#176527, @imp wrote:

Looks good to me, but maybe you'd do the file_loadraw() one first...

The kernel often has to get loaded first in order to do other operations.
For example, in the case of having the loader.rc file load a FDT blob, it will not let you do that if the kernel has not been loaded already.

Or did you mean the mfs_root and kernel modules load before the loader.rc?

[imp]

In D8494#176546, @stevek wrote:

In D8494#176527, @imp wrote:

Looks good to me, but maybe you'd do the file_loadraw() one first...

The kernel often has to get loaded first in order to do other operations.
For example, in the case of having the loader.rc file load a FDT blob, it will not let you do that if the kernel has not been loaded already.

Or did you mean the mfs_root and kernel modules load before the loader.rc?

I'm afraid I wasn't clear because it wasn't either of those things.

I'm thinking you should separate this change into two changes. One that's the file_loadraw() change. And a second one that's the rest of this diff. The code itself is fine. Sorry for the confusion.

[stevek]

In D8494#176547, @imp wrote:

I'm afraid I wasn't clear because it wasn't either of those things.

I'm thinking you should separate this change into two changes. One that's the file_loadraw() change. And a second one that's the rest of this diff. The code itself is fine. Sorry for the confusion.

Oh, okay, sure. I'll do those as separate commits.