cmd/link: generate manifest in EXE files

[quentinmit]

On Windows 10 and later, apps can opt into long path support by embedding an XML manifest:

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx

We should automatically embed this manifest when linking EXE files. For prior art, see this third-party tool for generating a .syso file containing a manifest:

josephspurrier/goversioninfo@f8c5d36#diff-88fef3681df95cd75f2ac89251404081

[minux]

are you proposing to just generate manifest to opt in long path support or add linker argument to let the user specify a custom manifest file? the later seems more generally useful, but I'm fine with just doing the first too.

[quentinmit]

I'm proposing the former for a start, since it doesn't require any UI changes.

Presumably any fix should continue to allow a user-specified .syso file to override the manifest.

[minux]

Do you propose to merge the user manifest with the built-in one or completely disable the built-in one when user has specified one?

[alexbrainman]

We should automatically embed this manifest when linking EXE files. For prior art, see this third-party tool for generating a .syso file containing a manifest:

It is probably not important, but do you plan to generate .syso file with the manifest and link it with the executable, or modify linker to append manifest as executable is built?

Alex