PARQUET-956: Specify BUILD_BYPRODUCTS for gtest

Author: Uwe L. Korn <uwe@apache.org>

Closes #301 from xhochy/PARQUET-956 and squashes the following commits:

ea4b7cf [Uwe L. Korn] PARQUET-956: Specify BUILD_BYPRODUCTS for gtest
diff --git a/cmake_modules/ThirdpartyToolchain.cmake b/cmake_modules/ThirdpartyToolchain.cmake
index 15a20bd..2b31e97 100644
--- a/cmake_modules/ThirdpartyToolchain.cmake
+++ b/cmake_modules/ThirdpartyToolchain.cmake
@@ -281,6 +281,7 @@
       # BUILD_BYPRODUCTS is a 3.2+ feature
       ExternalProject_Add(googletest_ep
         URL "https://github.com/google/googletest/archive/release-${GTEST_VERSION}.tar.gz"
+        BUILD_BYPRODUCTS ${GTEST_STATIC_LIB} ${GTEST_MAIN_STATIC_LIB}
         CMAKE_ARGS ${GTEST_CMAKE_ARGS})
     else()
       ExternalProject_Add(googletest_ep