[Document]Mention --ignore-space-at-eol in patching.md

[Pospelove]

My attempt to patch winpcap port resulted in a huge patch file full of whitespace changes.
--ignore-space-at-eol option forces git diff to ignore such whitespaces.

https://git-scm.com/docs/diff-options

--ignore-space-at-eol
Ignore changes in whitespace at EOL.

[JackBoosY]

If the patch generated using this option does not affect the application of this patch, I think we can accept it.

[Pospelove]

@JackBoosY In most cases this option does nothing, but in the case with different line endings, --ignore-space-at-eol reduces the size of a generated patch by just ignoring changes in whitespaces. Yes, vcpkg, obviously, succeeds to apply patches, generated with this option (vcpkg_apply_patches, vcpkg_from_github, etc)

[take5v]

Be aware, that git apply --ignore-whitespace and git diff -w (or --ignore-all-space) are broken, see https://stackoverflow.com/questions/66221977/git-apply-ignore-whitespace-is-broken and https://stackoverflow.com/questions/66221885/git-diff-w-or-ignore-all-space-is-broken. Tried on the latest git 2.36.0.windows.1 and get an error when vcpkg is applying a patch.

[JackBoosY]

@take5v Can you please provide a output log here?

[take5v]

@JackBoosY I tried steps described in a tutorial: https://vcpkg.readthedocs.io/en/latest/examples/patching/.

When I run git diff --ignore-space-at-eol | out-file -enc ascii foo.patch and then run vcpkg I get an error error: patch failed ... patch does not apply
However, when I run git diff | out-file -enc ascii foo.patch then git successfully applied and no errors from vcpkg.

Tested only on Windows so far (git 2.36.0.windows.1)