[LibFuzzer] Fix `-Wcomment` warning emitted by GCC.

```
./FuzzerIOWindows.cpp:185:1: warning: multi-line comment [-Wcomment]
 // Parse a directory ending in separator, like: SomeDir\
 ^
./FuzzerIOWindows.cpp:200:1: warning: multi-line comment [-Wcomment]
 // Parse a servername and share, like: SomeServer\SomeShare\
 ^
```

Differential Revision: https://reviews.llvm.org/D35244

llvm-svn: 307687