[C++] Release verification script fails with if CMAKE_INSTALL_LIBDIR is not $ARROW_HOME/lib

[asfimport]

Fix up shortly

Reporter: Phillip Cloud / @cpcloud
Assignee: Phillip Cloud / @cpcloud

PRs and other links:

• GitHub Pull Request #1762

_{Note: This issue was originally created as ARROW-2321. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1762
#1762