iox-eclipse-iceoryx#1758 Prevent to build googletest when GTest_DIR is defined

If GTest_DIR is defined with cmake parameters by users,
It means that the external googletest version will be used.
So, Downloading and building GoogleTest is not necessary.

Author: dongilchang

cmake/googletest/CMakeLists.txt

@@ -17,7 +17,7 @@
 cmake_minimum_required(VERSION 3.16)
 project(googletest-build CXX)
 
-if(BUILD_TEST)
+if(BUILD_TEST AND NOT GTest_DIR)
 
     # set download config, source and build paths
     set(DOWNLOAD_CONFIG_DIR ${CMAKE_BINARY_DIR}/dependencies/googletest/download)

doc/website/release-notes/iceoryx-unreleased.md

@@ -94,6 +94,7 @@
 - `ReleativePointer::registerPtr` returns `cxx::optional` [\#605](https://github.com/eclipse-iceoryx/iceoryx/issues/605)
 - `cxx::function` is no longer nullable [\#1104](https://github.com/eclipse-iceoryx/iceoryx/issues/1104)
 - Renamed `BaseRelativePointer` to `UntypedRelativePointer` [\#605](https://github.com/eclipse-iceoryx/iceoryx/issues/605)
+- Prevent building GoogleTest when `GTest_DIR` is defined [\#1758](https://github.com/eclipse-iceoryx/iceoryx/issues/1758)
 
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