x86_64-windows-gnu build issue with docgen

[F3real]

Running:

.\build.bat x86_64-windows-gnu baseline

fails with:

run docgen (langref.html): error: thread 18600 panic: start index 43 is larger than end index 42
C:\Users\user\zig-bootstrap\zig\tools\docgen.zig:985:32: 0x7ff776fd2522 in tokenizeAndPrintRaw__anon_5565 (docgen.exe.obj)
        if (mem.indexOf(u8, src[index..token.loc.start], "//")) |comment_start_off| {
                               ^
C:\Users\user\zig-bootstrap\zig\tools\docgen.zig:1225:31: 0x7ff776fd81c5 in tokenizeAndPrint__anon_5637 (docgen.exe.obj)
    return tokenizeAndPrintRaw(allocator, docgen_tokenizer, out, source_token, raw_src);
                              ^
C:\Users\user\zig-bootstrap\zig\tools\docgen.zig:1233:37: 0x7ff776fd9412 in printSourceBlock__anon_5652 (docgen.exe.obj)
        .zig => try tokenizeAndPrint(allocator, docgen_tokenizer, out, syntax_block.source_token),
                                    ^
C:\Users\user\zig-bootstrap\zig\tools\docgen.zig:1370:37: 0x7ff776fe0777 in genHtml__anon_4754 (docgen.exe.obj)
                try printSourceBlock(allocator, tokenizer, out, syntax_block);
                                    ^
C:\Users\user\zig-bootstrap\zig\tools\docgen.zig:106:16: 0x7ff776feeebf in main (docgen.exe.obj)
    try genHtml(allocator, &tokenizer, &toc, buffered_writer.writer(), zig_exe, opt_zig_lib_dir, do_code_tests);
               ^
C:\Users\user\zig-bootstrap\zig\lib\std\start.zig:348:65: 0x7ff776ff0c0c in WinStartup (docgen.exe.obj)
    std.os.windows.kernel32.ExitProcess(initEventLoopAndCallMain());
                                                                ^
???:?:?: 0x7ffd23da257c in ??? (KERNEL32.DLL)
???:?:?: 0x7ffd25c2aa57 in ??? (ntdll.dll)

run docgen (langref.html): error: the following command exited with error code 3:
C:\Users\user\zig-bootstrap\zig\zig-cache\o\a152e1b5eb0177590ea1068142cc0107\docgen.exe --zig C:\Users\user\zig_all\zig-bootstrap\out-win\host\bin\zig.exe C:\Users\user\zig-bootstrap\zig\doc\langref.html.in C:\Users\user\zig-bootstrap\zig\zig-cache\o\b99dc806ffa5ac9e6567db503607f3a0\langref.html