Don't add extra passes into the function pass manager

Exception for specific cases like linting, additional passes should
be going into the module pass manager (even if they are function
passes). The separate function pass manager is only used for very
early optimization passes.

Rather than apparending passes to the MPM, use the OptimizerLast
and EnabledOnOptLevel0 pass manager builder extension hooks, which
allow adding passes directly before finalization (alias
canonicalization and name-anon-globals).

The main effect and purpose of this change is to add sanitizer
passes at the end of the pipeline, which is where they belong.
In LLVM 9 the address sanitizer can't be used as a pass in the
early function pass manager, because it has a dependence on a
module-level analysis pass.

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1668,6 +1668,9 @@ extern "C" {
     pub fn LLVMRustPassKind(Pass: &Pass) -> PassKind;
     pub fn LLVMRustFindAndCreatePass(Pass: *const c_char) -> Option<&'static mut Pass>;
     pub fn LLVMRustAddPass(PM: &PassManager<'_>, Pass: &'static mut Pass);
+    pub fn LLVMRustAddLastExtensionPasses(PMB: &PassManagerBuilder,
+                                          Passes: *const &'static mut Pass,
+                                          NumPasses: size_t);
 
     pub fn LLVMRustHasFeature(T: &TargetMachine, s: *const c_char) -> bool;