Update double-conversion to version 3.1.7 / rev 11 via SR 943528
https://build.opensuse.org/request/show/943528
by user pgajdos + dimstar_suse
- update to 3.1.7:
* Reintroduce macros, if DOUBLE_CONVERSION_NON_PREFIXED_MACROS is set
* Also add support for Synopsys ARC64 architecture (forwarded request 943179 from dirkmueller)