Allow bison parsers to be generated as libraries

[Baltoli]

Fixes #3258

This PR is related to my ongoing work towards documenting "K as a library" (i.e. using the LLVM backend to generate libraries users can use to build their own tools, rather than relying on the K scripts to run their programs. One missing link in the existing toolchain that I identified was generating KORE from a surface program; doing so currently would require the user to shell out to one of the bison-generated parsers. This PR makes a small improvement to that workflow by allowing the bison parsers to be generated as shared libraries rather than as executables; the parser libraries can then be shipped alongside the C bindings libraries for user definitions.

After this PR, users will be able to run something like:

$ kompile test.k -v             \
  --gen-glr-bison-parser        \
  --bison-parser-library        \
  --llvm-kompile-type c         \
  --llvm-kompile-output libfoo.so

to generate a pair of shared libraries (libfoo.so, libparse_KItem_TEST.so) that provide an LLVM backend runtime and GLR Bison parser, respectively. These can then be embedded into an application.

The changes in this PR are as follows:

• Update the Bison wrapper code to use a similar "file or buffer" abstraction to the LLVM backend's writer type; this lets us output to a file directly as before for best performance, but also to keep the parsed KORE in memory if required.
• Add some preprocessor definitions that create a function char *parse_SORT(...) as well as the existing bison main entrypoint.
• Add frontend flags that generate the library following the syntax above.
• Add a custom integration test that links a small application against a generated parser and calls it in library mode.

[dwightguth]

I'd like to review this, but I might not get to it until next week. Is this blocking anything currently?

[Baltoli]

I'd like to review this, but I might not get to it until next week. Is this blocking anything currently?

No, I'm only using it in the context of my own work on a blog post; I'm using kup overrides to point the project at branches so there's absolutely no rush at all to review. Enjoy your week!

[radumereuta]

A few questions.
Java part looks fine.
The C part I'm not that familiar with.

[theo25]

I went over the C code and the regression test and it all looks good to me.