REGRESSION(r137994): It made JSC tests hang and layout tests fail on ARM Thumb2 / Linux
https://bugs.webkit.org/show_bug.cgi?id=108632

Patch by Simon Hausmann <simon.hausmann@digia.com> on 2013-02-27
Reviewed by Csaba Osztrogonác.

It appears that mprotect() is very slow on ARM/Linux, so disable the
approach of unreserved mappings there and fall back to overcomitting
memory, based on Uli Schlachter's recommendation.

* wtf/OSAllocatorPosix.cpp:
(WTF::OSAllocator::reserveUncommitted):
(WTF::OSAllocator::decommit):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144170 268f45cc-cd09-0410-ab3c-d52691b4dbfc