[clang-format] throws an incorrect assertion in consumeToken() formatting the MSVC stl

Summary:
An incorrect assertion is thrown when clang-formatting MSVC's STL library

```
Assertion failed: !Line.startsWith(tok::hash), file C:/llvm/llvm-project/clang/lib/Format/TokenAnnotator.cpp, line 847
Stack dump:
0.      Program arguments: C:\llvm\build\bin\clang-format.exe -i -n ./stl/inc/xkeycheck.h
```

```
Enable warning C4005 to find the forbidden define.
```

Reviewers: mitchell-stellar, STL_MSFT, klimek, krasimir

Reviewed By: mitchell-stellar

Subscribers: cfe-commits

Tags: #clang-format, #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D68707

llvm-svn: 374399