Simplify the setup leading to the testing of ReadMemory(),...

Simplify the setup leading to the testing of ReadMemory(), ReadCStringFromMemory(), and ReadUnsignedFromMemory().
Instead of getting the location of the variable and converting the hex string to an int, just use
val.AddressOf().GetValueAsUnsigned() to compute the address of the memory region to read from.

llvm-svn: 146719