ART: Convert pointer size to enum

Move away from size_t to dedicated enum (class).

Bug: 30373134
Bug: 30419309
Test: m test-art-host
Change-Id: Id453c330f1065012e7d4f9fc24ac477cc9bb9269
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index 3269dc6..4a4b98c 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -137,7 +137,7 @@
 
 size_t CodeGenerator::GetCachePointerOffset(uint32_t index) {
   auto pointer_size = InstructionSetPointerSize(GetInstructionSet());
-  return pointer_size * index;
+  return static_cast<size_t>(pointer_size) * index;
 }
 
 uint32_t CodeGenerator::GetArrayLengthOffset(HArrayLength* array_length) {