[clang] #include <//foo.h> incorrectly normalized to #include <foo.h>

[zygoloid]

Clang weirdly accepts for example

#include <//stddef.h>

but rejects with any other number of leading /s other than zero. It looks like something may be going wrong with the normalization of // -> / that is resulting in zero slashes at the start of the filename.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Richard Smith (zygoloid)

Clang weirdly accepts for example ```c++ #include <//stddef.h> ``` but rejects with any other number of leading `/`s other than zero. It looks like something may be going wrong with the normalization of `//` -> `/` that is resulting in zero slashes at the start of the filename.

[AaronBallman]

The issue does not reproduce on Windows (unsurprisingly given the difference in directory separators).