[AddressSpace] Use the macro to set hidden visibility on LocalAddressSpace.

[cdavis5x]

Summary

That attribute has no effect on Windows anyway--classes are hidden by
default.

[rnk]

lgtm

src/AddressSpace.hpp

#if defined(_LIBUNWIND_ARM_EHABI)
   uintptr_t       arm_section_length;
 #endif
 };
 
 
 /// LocalAddressSpace is used as a template parameter to UnwindCursor when
 /// unwinding a thread in the same process.  The wrappers compile away,
 /// making local unwinds fast.
-class __attribute__((visibility("hidden"))) LocalAddressSpace {
+class _LIBUNWIND_HIDDEN LocalAddressSpace {
 public:
   typedef uintptr_t pint_t;
   typedef intptr_t  sint_t;
   uint8_t         get8(pint_t addr) {
     uint8_t val;
     memcpy(&val, (void *)addr, sizeof(val));
     return val;
   }