Fat LTO ignores user GCC flags #1020

In my MIPS program, I have GCC flags specifically to disable $gp-relative accesses, which works fine without LTO enabled. But if I enable LTO, it starts compiling with $gp-relative accesses/relocations, which breaks the entire build at the linking stage.

After some investigation, I figured out that this piece of code may be the culprit. It seems like it creates a new gccjit context and only sets a few arguments (disregarding whatever I set in llvm_args) before it starts compiling.

https://github.com/rust-lang/rustc_codegen_gcc/blob/master/src/back/write.rs#L146