[compiler-rt][ORC] Silence warning when building on MSVC/Windows

This fixes (the ORC lib already builds with exceptions disabled):
```
[5/11] Building CXX object projects\compiler-rt\lib\orc\CMakeFiles\RTOrc.x86_64.dir\dlfcn_wrapper.cpp.obj
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.38.33130\include\vector(1619): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
```