debug/pe: pe.Open fails on object files produced by llvm-mingw 21 [1.24 backport]

[gopherbot]

@ianlancetaylor requested issue #75219 to be considered for backport to the next 1.24 minor release.

@gopherbot Please open backport issues.

This is a problem that reportedly arises when using the new clang21 release on mingw. It should be fixed on open releases.