BUILD_DIR in CMakeLists

Hello everyone. I just added a cmake variable, BUILD_DIR, to the various system tests’ CMakeLists.txt files. It allows you to specify the directory that the executable binaries will be written to (it can create the directory if needed, but won’t create a subdirectory if the intended parent directory doesn’t exist).

Before, the directory was taken from CMAKE_BUILD_TYPE; that is, if BasicSystemTest had CMAKE_BUILD_TYPE=Debug, the executable would be BasicSystemTest/Debug/BasicSystemTest, etc.

Now, if BUILD_DIR is empty, the directory is taken from CMAKE_BUILD_TYPE as before. But if BUILD_DIR is not empty, it will use that as the directory instead. You can specify an absolute path, or a relative path; relative paths are relative to CMAKE_CURRENT_SOURCE_DIR, which in the BasicSystemTest example would be BasicSystemTest.