tidy errors don't abort make -jn

[catamorphism]

Write code with long lines, run make check -j12, ignore the tidy errors because everything has scrolled too far and tidy won't abort the build when running with -j, check in code with tidy errors. This has happened to me at least once.

I'm not sure if this is an inherent limitation of make, but maybe it's another reason to rewrite the build system in Rust?

[graydon]

$ make -j 20 check
cfg: shell host triple x86_64-unknown-linux-gnu
cfg: host for x86_64-unknown-linux-gnu is x86_64
cfg: unix-y environment
cfg: using gcc
cfg: no llnextgen found, omitting grammar-verification
cfg: including dist rules
cfg: including test rules
check: formatting
compile_and_link: x86_64-unknown-linux-gnu/stage0/lib/rustc/x86_64-unknown-linux-gnu/lib/libcore.so
extract: tutorial tests
extract: tutorial-ffi tests
extract: tutorial-macros tests
extract: tutorial-borrowed-ptr tests
extract: tutorial-tasks tests
extract: ref tests
/home/graydon/src/rust/src/libcore/core.rs:76: tab character
/home/graydon/src/rust/src/libcore/core.rs:76: trailing whitespace
make: *** [tidy] Error 123
make: *** Waiting for unfinished jobs....
$

Wfm in this case. Maybe run builds with make -j 20 || echo "ERROR" ? In any case, we are definitely rewriting it in rust asap (I know "asap" seems to mean "in quite a while" around here) so I'm going to close this as a dupe of #2237 / #2238.