`FIH_LABEL` fails with lld

[d3zd3z]

The LLVM linker supports fairly aggressive dead code elimination. The way we are inserting labels for the FIH tools, causes the LLVM linker to consider various blocks of following code to be dead and eliminates them. The result is code that executes somewhat nonsensically, and in a way that is difficult to debug.

#1980 adds a workaround for Apple targets by just not inserting the labels, but it would be nice to figure out a way to add these that the LLVM linker doesn't eliminate.