[vcpkg | vcpkg_copy_pdbs]: Support copying .pdb when using llvm/clang-mingw

[past-due]

Describe the pull request

Clang-based mingw toolchains can support generating .PDB files (example: https://github.com/mstorsjo/llvm-mingw/blob/master/README.md#pdb-support )

However, the existing vcpkg_copy_pdbs function does not support this.

This PR makes two core changes / additions to vcpkg_copy_pdbs:

1. Always support trying dumpbin /PDBPATH when the host is Windows (even if using a mingw toolchain)
2. Support a backup path to find the .pdb files when cross-compiling with mingw (or if dumpbin fails or cannot be found, which may happen - even on Windows - depending on how PATHS are set up for use with the mingw toolchain).

• Which triplets are supported/not supported? Have you updated the CI baseline?

  windows / mingw, No updates needed

• Does your PR follow the maintainer guide?

  Yes

[Neumann-A]

Consider taking a look at:
https://github.com/microsoft/vcpkg/pull/25692/files#diff-8b5de3c96a4458bb5c63401b7278e36fb78f0f7aad949780353bec0b1f6e4c77

[JonLiu1993]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[vicroms]

Hi @past-due

We've been actively trying to remove our dependency on dumpbin by implementing the features we need directly in the vcpkg executable (see this PR to remove dumpbin calls and the changes to replace applocal.ps1).

Would you be willing to investigate whether we can get the PDB path information using a method that would not require dumpbin?

These seem like good starting points:

• PE Format - Debug Directory
• .NET implementation of PEReader

[past-due]

@vicroms If you are already parsing the PE header, I believe:

• If you get the IMAGE_OPTIONAL_HEADER,
• use that to get the pointer to the IMAGE_DEBUG_DIRECTORY (DataDirectory[IMAGE_DIRECTORY_ENTRY_DEBUG]?)
• then if IMAGE_DEBUG_DIRECTORY.Type == IMAGE_DEBUG_TYPE_CODEVIEW, cast <base image address> + IMAGE_DEBUG_DIRECTORY.AddressOfRawData to a CodeView debugging information struct*

Which I believe takes a form like (from various snippets around the web):

struct CodeViewDebuggingInfo
{
  DWORD Signature;
  BYTE Guid[16];
  DWORD Age;
  char PdbFileName[0]; // presumably this is null-terminated? Probably a good idea to check `IMAGE_DEBUG_DIRECTORY.SizeOfData`
};

(Completely untested and unverified, but hopefully that helps point in a useful direction.)

I still think there's probably merit to keeping the fallback that this PR adds (which is to just search for a matching .pdb file in the same directory) as well.

[JonLiu1993]

Closing this PR since it seems that no progress is being made. Please ping us to reopen if work is still being done.