add on HermizCore an additional lock to protect static data

…eeded

This is a bit unfortunate, but code needs to be able to fatally error
early on (in particular, syntax_pos after we move SourceMap there). It's
also a tiny bit of code, which means it's ultimately not that bad.

This does not update the use sites or delete the now unnecessary
SourceMapper trait, to allow git to interpret the file move as a rename
rather than a new file.

SourceMap is now in the root of all rustc-specific crates, syntax_pos,
so there's no need for the trait object to decouple the dependencies
between librustc_errors and libsyntax as was needed previously.

Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>

protect creation of destructors by a mutex

- add on HermitCore an additional lock to protect static data

Add more tests for fixed ICEs

Closes rust-lang#36122 (fixed in 1.20.0)
Closes rust-lang#58094 (fixed in rust-lang#66054)
Also, fix mistaken test case, from rust-lang#30904 to rust-lang#30906 (cc @eddyb)

r? @Centril

…excrichton

Add --force-run-in-process unstable option to libtest

When running tests with `-Zpanic_abort_tests`, it's sometimes desirable to fall back to the old behavior of only running tests in-process. This comes in handy if the system process launcher is unavailable, or the test code somehow expects all tests to be run in the same process.

For example, in Fuchsia we have unit tests that actually test the process launcher itself, in which case we can't use the process launcher to run the tests :).

r? @alexcrichton
cc @cramertj,@petrhosek

Move the JSON error emitter to librustc_errors

This is done both as a cleanup (it makes little sense for this emitter to be in libsyntax), but also as part of broader work to decouple Session from librustc itself.

Along the way, this also moves SourceMap to syntax_pos, which is also nice for the above reasons, as well as allowing dropping the SourceMapper trait from code. This had the unfortunate side-effect of moving `FatalError` to rustc_data_structures (it's needed in syntax_pos, due to SourceMap, but putting it there feels somehow worse).

libpanic_unwind for Miri: make sure we have the SEH lang items when needed

r? @oli-obk  @alexcrichton This is required to fix the Miri toolstate. Turns out rustc complains when doing codegen for MSVC and these lang items do not exist. For now `cfg(miri)` needs to still be able to codegen (we [plan to change that](rust-lang/miri#1048 (comment)) but that's a larger project requiring improvements to xargo and maybe also cargo; that should not block fixing the toolstate). Yes, this is a hack, but it is inside `cfg(miri)` so I hope this is okay.

Cc @Aaron1011