Fix gdb.dwarf2/dw2-double-set-die-type.exp with Clang

Fix gdb.dwarf2/dw2-double-set-die-type.exp with Clang

gdb.dwarf2/dw2-double-set-die-type.exp failed to build with Clang,
because of the following issues:

- One .uleb128 directive was specified with an uppercase U,
  causing Clang to fail with the message:
    error: unknown directive
  This commit converts that directive to all-lowercase.

- The label ".Labbrev1_begin" was referenced but not defined,
  causing Clang to fail with the message:
    <unknown>:0: error: Undefined temporary symbol
  This commit adds the label in the appropriate place.

- The label ".Ldebug_line0" was referenced but not defined,
  causing Clang to fail with the message:
    <unknown>:0: error: Undefined temporary symbol
  This commit removes the reference.

gdb/testsuite/ChangeLog:

	* gdb.dwarf2/dw2-double-set-die-type.S (.Ldie_3e0):
	Convert directive to lowercase.
	(.Labbrev1_begin): Add missing label.
	(abbrev code 0x1): Remove DW_AT_stmt_list.
	(.Ldie_b): Likewise.