Incorrect `__LINE__` with `-frewrite-includes` and mixed CRLF

[slonopotamus]

Way to reproduce

Create 1.cpp (CRLF line endings)

#include "1.h"

Create 1.h (LF line endings, whitespace is important)

    #if 1
static_assert(__LINE__ == 2, "");
    #endif

Try to compile

$ clang++ -E -frewrite-includes 1.cpp | clang++ -c -x c++ -
In file included from 1.cpp:1:
./1.h:3:1: error: static assertion failed due to requirement '3 == 2': 
static_assert(__LINE__ == 2, "");
^             ~~~~~~~~~~~~~
1 error generated.

Tested on

clang version 15.0.5
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm/15/bin
Configuration file: /etc/clang/clang++.cfg

and

clang version 13.0.1
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: <redacted>

Additional info

Bug doesn't reproduce if -frewrite-includes is omitted.

Bug doesn't reproduce if whitespace in front of #if 1 is removed.

Bug doesn't reproduce if both 1.h and 1.cpp have same line endings.

Bug reproduces if CRLF/LF is swapped - 1.cpp has LF and 1.h has CRLF.

Bug reproduces if whitespace in front of #if 1 is replaced with TAB.

[shafik]

CC @cor3ntin @tahonermann

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[llvmbot]

@llvm/issue-subscribers-good-first-issue

[tahonermann]

Proposed patch submitted for code review: https://reviews.llvm.org/D140984.