DWARFv5: Info address command error in gdb with DWARFfv5.

DWARFv5: Info address command error in gdb with DWARFfv5.

GDB throws the error 'Unrecognized DWARF opcode 0x02 at 2' when running
Info address command with the executable file compiled with -gdwarf-5 flag.
This patch fixes this error.

Tested by running the testsuite before and after the patch and there is
no increase in the number of test cases that fails. Tested with both
-gdwarf-4 and -gdwarf-5 flags. Also tested -gslit-dwarf along with
-gdwarf-4 as well as -gdwarf-5 flags. Used clang version 10.0.0.
This is the test case used-

void bar(int arr[], int l, int m, int r) {
    int i, j, k, n1= m - l + 1, n2= r - m, L[n1], R[n2];
    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1+ j];
}

int main()
{
    int arr[] = {12, 11};
    bar(arr,0,1,2);
    return 0;
}

clang -gdwarf-5 test.c -o test.out

gdb test.out
gdb> start
gdb> step
gdb> step
gdb> step
gdb> step
gdb> info address L
Symbol "L" is multi-location:
  Range 0x7c04007902bc5084-0x67fb876440700: a complex DWARF expression:
     0: DW_OP_breg16 1 [$rip]
Unrecognized DWARF opcode 0x02 at 2

gdb/ChangeLog:
2020-04-07  Nitika Achra  <Nitika.Achra@amd.com>

	* dwarf2/loc.c (loclist_describe_location): Call the function decode_debug_loclists_
	addresses if DWARF version is 5 or more because DW_LLE_start* or DW_LLE_offset_pair
	with DW_LLE_base_addressx are being emitted in DWARFv5.
	Add the newly added kind DW_LOC_OFFSET_PAIR also.
	The length of location description is an unsigned ULEB integer in DWARFv5 instead of
	unsigned integer.