[ORC] Force linking of eh-frame registration functions from LLJIT.cpp.

Since aedeb8d5, which switched to EPC-based eh-frame registrationin LLJIT,
the eh-frame registration functions need to be forcibly linked into the target
process.

Failure to link the eh-frame registration functions triggered a test failure in
https://green.lab.llvm.org/green/job/clang-stage1-RA/31497, which was fixed by
forcibly linking the registration functions into that test case in saf2b2214
(rdar://101083784), however it has also caused some tests (e.g. the C API unit
tests) that depend on successful construction of an LLJIT instance to be
skipped.

Moving the forcible registration into LLJIT.cpp fixes the general issue.