[JSC] Do not generate an Add when adding a zero immediate to something

[JSC] Do not generate an Add when adding a zero immediate to something
https://bugs.webkit.org/show_bug.cgi?id=151171

Patch by Benjamin Poulain <bpoulain@apple.com> on 2015-11-12
Reviewed by Geoffrey Garen.

Avoid generating an add if one of arguments is a zero immediate.

On x86, the add32/64() were also used internally for branchAdd32/64.
I split the code that sets flag to add32AndSetFlags() to make sure
we always force the flags before testing.

I could have used CMp to set the flags but I would gain nothing from
that, cmp is just a SUB.

* assembler/MacroAssemblerARM64.h:
(JSC::MacroAssemblerARM64::add32):
(JSC::MacroAssemblerARM64::add64):
* assembler/MacroAssemblerARMv7.h:
(JSC::MacroAssemblerARMv7::add32):
* assembler/MacroAssemblerX86.h:
(JSC::MacroAssemblerX86::add32):
* assembler/MacroAssemblerX86Common.h:
(JSC::MacroAssemblerX86Common::add32):
(JSC::MacroAssemblerX86Common::branchAdd32):
(JSC::MacroAssemblerX86Common::add32AndSetFlags):
* assembler/MacroAssemblerX86_64.h:
(JSC::MacroAssemblerX86_64::add32):
(JSC::MacroAssemblerX86_64::add64):
(JSC::MacroAssemblerX86_64::branchAdd64):
(JSC::MacroAssemblerX86_64::add64AndSetFlags):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@192409 268f45cc-cd09-0410-ab3c-d52691b4dbfc