Fix GetGlobalVariableOffset with tagged pointer in aarch64

Tagged pointer for aarch64 since Android R would lead top byte to have
random values. For example of a symbol from libart.so in a hwasan
enabled device in Android R:

1490: 8800000000b094a0   144 OBJECT  GLOBAL 24 __dex_debug_descriptor

We need to mask off the top byte so that the address range comparison
would work as intended.

Test: Ran new unit test

Signed-off-by: Yong Li <yongl0722@gmail.com>
Change-Id: Ia8c638e16baff57740c569e9eaf9cfd1f5bd3fad