Rename Abort terminator to Terminate

Unify terminology used in unwind action and terminator, and reflect
the fact that a nounwind panic is triggered instead of an immediate
abort is triggered for this terminator.

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -73,7 +73,7 @@ pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     /// Cached unreachable block
     unreachable_block: Option<Bx::BasicBlock>,
 
-    /// Cached double unwind guarding block
+    /// Cached terminate upon unwinding block
     terminate_block: Option<Bx::BasicBlock>,
 
     /// The location where each MIR arg/var/tmp/ret is stored. This is