[gdb/testsuite] templates.exp to accept clang++ output

[gdb/testsuite] templates.exp to accept clang++ output

Please consider below testcase with intended error.
``````````
    constexpr const char cstring[] = "Eta";
    template <const char*, typename T> class Column {};
    using quick = Column<cstring,double>; // cstring without '&'

    void lookup() {
      quick c1;
      c1.ls();
    }
``````````
It produces below error.
``````````
no member named 'ls' in 'Column<&cstring, double>'.
``````````
Please note that error message contains '&' for cstring, which is absent
in actual program.
Clang++ does not generate & in such cases and this should also be
accepted as correct output.

gdb/testsuite/ChangeLog:

	* gdb.cp/templates.exp: Accept different but correct output
	from the Clang++ compiled binary also.