Fix duplicate label in gdb.dwarf2/dw2-op-out-param.S

Fix duplicate label in gdb.dwarf2/dw2-op-out-param.S

gdb.dwarf2/dw2-op-out-param.S contained a duplicate label, and failed
to build with clang with the following error:

 gdb compile failed, /gdbtest/src/gdb/testsuite/gdb.dwarf2/dw2-op-out-param.S:163:1:
       error: invalid symbol redefinition
 .Ltext5:
 ^

This commit renames the two labels as .Ltext5a and .Ltext5b, and
updates all references appropriately.

gdb/testsuite/ChangeLog:

	* gdb.dwarf2/dw2-op-out-param.S (.Ltext5): Fix duplicate label.