C++: Enable library builds for 3rd-party users without having to build thirdparty googletest

[asfimport]

While the thirdparty dependencies for libarrow may not always remain so minimal, for now it would be useful to have a library build option where only necessary thirdparty dependencies are built (currently there are none).

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-50. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
See

https://github.com/apache/arrow/blob/master/python/doc/INSTALL.md

from

6fdcd49

By following these instructions one can install Arrow C++ without building googletest