[CMake] Trigger the memory-reduction tricks on armhf too

[CMake] Trigger the memory-reduction tricks on armhf too
https://bugs.webkit.org/show_bug.cgi?id=146640

Patch by Emanuele Aina <emanuele.aina@collabora.com> on 2015-09-04
Reviewed by Csaba Osztrogonác.

* Source/cmake/OptionsCommon.cmake:
Activate --no-keep-memory even on armhf to reduce the amount of memory
needed during linking, to avoid out-of-memory failures as much as
possible.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@189344 268f45cc-cd09-0410-ab3c-d52691b4dbfc