gcc: build all languages at once?

[Sarah Morgensen <iskarian@mgsn.dev>]

Hello Guix,

I notice that out of GCC's supported languages (ada, c, c++, d, fortran,
go, jit, lto, objc, obj-c++) we currently build all except ada, and five
of them (d, fortran, go, objc, and obj-c++) are built separately.  Most
of GCC's build time is spent bootstrapping and building the actual
compiler, rather than building the frontends, so we would save a lot of
build time by building them all together.

We could also possibly reuse the 'core' parts of GCC between language
frontends, saving some space.  (This is what distros seem to do.)

If we do this, I'm not sure whether it would be better to have each
additional language as an output for gcc, or as a separate package.

Currently, the only build-time difference between our GCC packages is
that our package for 'jit' uses '--enable-host-shared', which
"[specifies] that the host code should be built into
position-independent machine code (with -fPIC), allowing it to be used
within shared libraries, but yielding a slightly slower compiler" [0].
I don't think it would be too big of a hit to just turn that on
unconditionally, but we could also keep 'jit' as a separately-built
package.

What do you all think?

[0] https://gcc.gnu.org/install/configure.html

--
Sarah