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ARROW-3778: [C++] Compile parts of test-util.h that we can once, link with unit tests

This has to be compiled into a separate static library and added to the link libs for the unit tests and benchmarks

Author: Wes McKinney <wesm+git@apache.org>

Closes #2997 from wesm/ARROW-3778 and squashes the following commits:

50cc8e2f4 <Wes McKinney> Use static test linkage in Windows Static CRT build
c3d5fe3d8 <Wes McKinney> Add ARROW_TEST_LINKAGE option so that ARROW_BUILD_SHARED is not forced to ON in Windows Static CRT build
452896a0d <Wes McKinney> clang-format, fix up Parquet linking again, fix benchmark linking
97d905c2c <Wes McKinney> Fix linking in Parquet tests
750f2e8f2 <Wes McKinney> Build auxiliary testing libraries as DLL to avoid symbol visibility linking issues on Windows
881e61f30 <Wes McKinney> Compile parts of test-util.h that we can once, link with unit tests