RustWrapper: adapt to LLVM change 0f45c16f2caa
RustWrapper: adapt to LLVM change 0f45c16f2caa

The above-mentioned commit (part of the LLVM 14 development cycle)
removes a method that rustc uses somewhat extensively. We mostly switch
to lower-level methods that exist in all versions of LLVM we use, so no
new ifdef logic is required in most cases.

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