Previously, it called `::operator new` which may throw `std::bad_alloc`,
regardless of whether LLVM itself was built with exception handling, and
this can cause safety issues if outside code has destructors that will
call back into LLVM. Now we use `::operator new(..., nothrow)` and call
`llvm::report_bad_alloc_error` when allocation fails, which will abort
when LLVM is built without exceptions.
Ref: https://github.com/llvm/llvm-project/issues/85281
There's an ABI breakage here if LLVM is compiled in C++14 without
aligned allocation and a user tries to use the result with aligned
allocation. If DenseMap or unique_function is used across that ABI
boundary it will break (PR45413). Moving it out of line is a bit of
a band-aid and LLVM doesn't really give ABI guarantees at this level,
but given the number of complaints I've received over this it still
seems worth fixing.
