Add initial support for DataFlowSanitizer

Adds initial support for DataFlowSanitizer to the Rust compiler. It
currently supports `-Zsanitizer-dataflow-abilist`. Additional options
for it can be passed to LLVM command line argument processor via LLVM
arguments using `llvm-args` codegen option (e.g.,
`-Cllvm-args=-dfsan-combine-pointer-labels-on-load=false`).

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -480,6 +480,9 @@ pub struct SanitizerOptions {
     pub sanitize_address: bool,
     pub sanitize_address_recover: bool,
     pub sanitize_cfi: bool,
+    pub sanitize_dataflow: bool,
+    pub sanitize_dataflow_abilist: *const *const c_char,
+    pub sanitize_dataflow_abilist_len: size_t,
     pub sanitize_kcfi: bool,
     pub sanitize_memory: bool,
     pub sanitize_memory_recover: bool,