Switch int8_t to GPRReg in StructureStubInfo because sizeof(GPRReg) == sizeof(int8_t)

Switch int8_t to GPRReg in StructureStubInfo because sizeof(GPRReg) == sizeof(int8_t)
https://bugs.webkit.org/show_bug.cgi?id=189166

Reviewed by Mark Lam.

* bytecode/AccessCase.cpp:
(JSC::AccessCase::generateImpl):
* bytecode/GetterSetterAccessCase.cpp:
(JSC::GetterSetterAccessCase::emitDOMJITGetter):
* bytecode/InlineAccess.cpp:
(JSC::getScratchRegister):
* bytecode/PolymorphicAccess.cpp:
(JSC::PolymorphicAccess::regenerate):
* bytecode/StructureStubInfo.h:
(JSC::StructureStubInfo::valueRegs const):
* jit/JITInlineCacheGenerator.cpp:
(JSC::JITByIdGenerator::JITByIdGenerator):
(JSC::JITGetByIdWithThisGenerator::JITGetByIdWithThisGenerator):
(JSC::JITInstanceOfGenerator::JITInstanceOfGenerator):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@235527 268f45cc-cd09-0410-ab3c-d52691b4dbfc