Centralize instruction-set pointer-size, alignment, 64b-width code
in instruction_set.h/cc

This allows to clean up some places that currently make explicit
comparisons.

Change-Id: I0dcc924c52fa53306f706aceea93a2d4a655c5df
diff --git a/runtime/instruction_set.h b/runtime/instruction_set.h
index a08becf..c746e06 100644
--- a/runtime/instruction_set.h
+++ b/runtime/instruction_set.h
@@ -35,6 +35,10 @@
 };
 std::ostream& operator<<(std::ostream& os, const InstructionSet& rhs);
 
+size_t GetInstructionSetPointerSize(InstructionSet isa);
+size_t GetInstructionSetAlignment(InstructionSet isa);
+bool Is64BitInstructionSet(InstructionSet isa);
+
 #if defined(__arm__)
 static constexpr InstructionSet kRuntimeISA = kArm;
 #elif defined(__aarch64__)