Missing tsan interceptor for _longjmp on Mac

There is an interceptor for `_setjmp` but not `_longjmp`. The causes `_longjmp` to fail to restore the `__tsan_func_entry`/`__tsan_func_exit` stack to its position at `_setjmp` and can eventually result in overflow and internal TSAN crashes.

Discovered when addressing https://github.com/dart-lang/sdk/issues/61536.

```c
#include

__attribute__((noinline))
void foo(jmp_buf* buf) {
_longjmp(*buf, 1);
}

int main() {
jmp_buf buf;
for (int i = 0; i < 10000000; i++) {
if (_setjmp(buf) == 0) {
foo(&buf);
}
}
}
```

This small example crashes with `_setjmp`/`_longjmp`, but works with `setjmp`/`longjmp`.

Start by locating the existing `_setjmp` interceptor and comparing it with the missing `_longjmp` path in the ThreadSanitizer runtime. Build and run the provided C reproducer on Mac, then verify that repeated `_setjmp`/`_longjmp` calls no longer cause stack overflow or an internal ThreadSanitizer crash.

Written by the indexing model from the issue text.