Support gdbclient.py on riscv64

Add the path to the existing architecture-specific runtime directory,
in preparation for when lldb-server is added to the toolchain build by
Iba7efaa62e7d3cc8e3bd1080d9b4a67bc241faf2.

Test: `gdbclient.py -r surfaceflinger` connected to a riscv64 board
Change-Id: I1654378a7ba92fcd7ffe478d2b491f426655e6f1
1 file changed