gdb: Disable hard-coding of library rpaths

gdb: Disable hard-coding of library rpaths

GDB's configury has a tendency to hard-code the path where it found
libexpat using "-Wl,--rpath".  This is undesirable and leads to QA warnings.

Fortunately, the helpful GDB maintainers have provided a "--disable-rpath"
switch to turn this behaviour off.  Let's use it and profit.

(From OE-Core rev: 3d70f28cc9612f733b835df139f31c197528677a)

Signed-off-by: Phil Blundell <philb@gnu.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>