build: Fix for building dist target outside of project root

[crass]

Motivation and Context

Most projects that build with autoconf allow having a build directory separate from the source root directory. This is currently broken in zfs. This can be verified by running the following commands from zfs source root:

./autogen.sh
ZFSSRC=$PWD
mkdir -p ../zfs-build
cd ../zfs-build
$PWD/configure --with-config=user
make dist

I ran across this failure when trying to build the rpm-utils target, which uses the dist target, from a build directory.

Description

Do not change the working directory when doing copying because $distdir is a path relative to the working directory, and thus not valid after changing the working directory. This previously worked, when configure was run from the project root, because @srcdir@ was the same as the build working directory.

How Has This Been Tested?

Using the command described above. I could be nice to have the CI tests build outside the source directory.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• [ x I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.