fix missing compiler_rt in release modes

the optimizer was deleting compiler_rt symbols, so I changed
the linkage type from LinkOnce to Weak

also changed LinkOnce to mean linkonce_odr in llvm and
Weak to mean weak_odr in llvm.

See #563
1828f8eb8eAndrew Kelley committed on 10/25/2017, 1:31:47 AMparentd7e28f9
17 files changedLine totals unavailable