The -runtime-counter-relocation switch is changed from a Boolean to a
three-way switch: none, variable, or function. The previous
-runtime-counter-relocation=true behavior is now selected with
-runtime-counter-relocation=variable. In the new ...=function mode,
instead of loading the global variable `__llvm_profile_counter_bias`,
instrumented code calls the function `__llvm_profile_counter_dynamic_bias`
with no arguments to return the bias. This can be a runtime function or
it can be defined in the translation unit to be inlined.