Set -funwind-tables and -fno-exceptions unconditionally for LLVM's libunwind
Set -funwind-tables and -fno-exceptions unconditionally for LLVM's libunwind

These are required otherwise libunwind will end up with undefined
references to __gxx_personality_v0 which is provided by C++ ABI
library and that's undesirable.

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust