[PM] Wire up support for writing bitcode with new PM.

This moves the old pass creation functionality to its own header and
updates the callers of that routine. Then it adds a new PM supporting
bitcode writer to the header file, and wires that up in the opt tool.
A test is added that round-trips code into bitcode and back out using
the new pass manager.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199078 91177308-0d34-0410-b5e6-96231b3b80d8

test/Other/new-pass-manager.ll

@@ -29,6 +29,11 @@
 ; CHECK-NOOP:   ret void
 ; CHECK-NOOP: }
 
+; Round trip through bitcode.
+; RUN: opt -f -o - -passes='no-op-module,no-op-module' %s \
+; RUN:     | llvm-dis \
+; RUN:     | FileCheck %s --check-prefix=CHECK-NOOP
+
 define void @foo() {
   ret void
 }