[NewPM][Sancov] Create the Sancov Pass after building the pipelines

We're running into linker errors from missing sancov sections:

```
ld.lld: error: relocation refers to a discarded section: __sancov_guards
>>> defined in user-arm64-ubsan-sancov-full.shlib/obj/third_party/ulib/scudo/scudo.wrappers_c.cc.o
>>> referenced by common.h:26 (../../zircon/third_party/ulib/scudo/common.h:26)
... many other references
```

I believe this is due to a pass in the default pipeline that somehow discards
these sections. The ModuleSanitizerCoveragePass was initially added at the
start of the pipeline. This now adds it to the end of the pipeline for
optimized and unoptimized builds.

Differential Revision: https://reviews.llvm.org/D67323

llvm-svn: 371326