[MIT-Scheme-devel] parallelizing the build

[Taylor R Campbell]

I just pushed some changes to make the native build safe for `make
-j'.  This should speed up the build a good deal on multicore systems.
It's very coarse-grained (directory-by-directory, not file-by-file),
so there's a limit to the factor by which it will speed up -- maybe 2
or 3 -- but that's still a lot better than before.

I haven't tested it heavily, but it seems to work for me.  Let me know
if I broke anything.

This is only the native build -- it does not apply to the liarc build
or the svm build, both of which are very much not safe for `make -j'.
Similar, but more complicated, changes will be required for those.

This does not restructure the build at all (except to split up
syntaxing and compiling runtime and edwin).  For example, it doesn't
make the current insane bootstrapping process more sensible, which is
something we'll want to do in the future, particularly for liarc and
svm (and in the distant future, for cross-builds without liarc or
svm).