Improve StringImpl code density for older ARM hardware
https://bugs.webkit.org/show_bug.cgi?id=114898

Reviewed by Geoffrey Garen.

Source/WebKit: 

* WebKit.vcxproj/WebKitExportGenerator/WebKitExports.def.in:

Source/WebKit/win: 

* WebKit.vcproj/WebKitExports.def.in:

Source/WTF: 

Reduce the number of instructions needed for StringImpl::deref
on older ARM hardware.

The extra indirection should have a negligible impact on x86_64.

* wtf/text/StringImpl.cpp:
(WTF::StringImpl::destroy):
* wtf/text/StringImpl.h:
(StringImpl):
(WTF::StringImpl::deref):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148857 268f45cc-cd09-0410-ab3c-d52691b4dbfc