gnucash master: Detect and flag MinGW64

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/18ef968f (commit)
	from  https://github.com/Gnucash/gnucash/commit/cb5e311a (commit)



commit 18ef968ff1284a1e9512fa1e32a84c7290f55fde
Author: John Ralls <jralls at ceridwen.us>
Date:   Sat Jul 22 13:28:01 2017 -0700

    Detect and flag MinGW64
    
    Got lost in the rebase and merge somehow.



Summary of changes:
 CMakeLists.txt | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)