gdb/testsuite: do not hard-code location indices in condbreak-multi-context.exp

gdb/testsuite: do not hard-code location indices in condbreak-multi-context.exp

Breakpoint locations are sorted according to their addresses.  The
addresses are determined by how the compiler emits the code.
Therefore, we may have a different order of locations depending on the
compiler we use.  To make the gdb.base/condbreak-multi-context.exp
test flexible enough for different compilers' output, do not hard-code
location indices.

Tested with GCC and Clang.

gdb/testsuite/ChangeLog:
2020-11-24  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* gdb.base/condbreak-multi-context.exp: Do not hard-code location
	indices.