i#2029: base-adjust the gdb command to load DR's symbols
i#2029: base-adjust the gdb command to load DR's symbols

libdynamorio.so's base was not adjusted for the load base for the gdb
add-symbol-file command.

Fixes #2029

Review-URL: https://codereview.appspot.com/315810043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio