gnucash maint: CMake: Test for & set WORDS_BIGENDIAN, set _GNU_SOURCE.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/766dc9b2 (commit)
	from  https://github.com/Gnucash/gnucash/commit/586cd704 (commit)



commit 766dc9b2d5cee4810a2d3a3b85091e1934f3d19f
Author: John Ralls <jralls at ceridwen.us>
Date:   Sat Sep 8 13:53:25 2018 -0700

    CMake: Test for & set WORDS_BIGENDIAN, set _GNU_SOURCE.
    
    Got lost in transition from autotools.



Summary of changes:
 CMakeLists.txt | 7 +++++++
 1 file changed, 7 insertions(+)