gnucash maint: Improve test building with the Xcode generator.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/33902a67 (commit)
	from  https://github.com/Gnucash/gnucash/commit/8fc901fb (commit)



commit 33902a6793dd11f4ee64189a47d735a548948a7d
Author: John Ralls <jralls at ceridwen.us>
Date:   Mon Mar 23 17:52:26 2020 -0700

    Improve test building with the Xcode generator.
    
    Add CONFIGURATIONS keyword to unadorned tests, enables tests with
    multi-config generators.
    Add CONFIGURATION generator expression to libgtest.a and libgmock.a
    build directory specs when building with Xcode so that it can
    find them when building tests.



Summary of changes:
 common/cmake_modules/GncAddTest.cmake      | 14 +++++++++++---
 libgnucash/backend/xml/test/CMakeLists.txt |  1 +
 libgnucash/engine/test/CMakeLists.txt      |  2 +-
 3 files changed, 13 insertions(+), 4 deletions(-)