[gdb/testsuite] Fix assembly comments in gdb.dwarf2/clang-debug-names.exp.tcl

[gdb/testsuite] Fix assembly comments in gdb.dwarf2/clang-debug-names.exp.tcl

On openSUSE Leap 15.2 aarch64 I ran into:
...
clang-debug-names-debug.S:72: \
  Error: junk at end of line, first unrecognized character is `#'
...
due to:
...
    71  .Ldebug_names_start:
    72    .short 5                      # Header: version
...

Fix this by using the /* ... */ comment style instead:
...
$ sed -i 's% #\([^"]*\)%/*\1 */%' clang-debug-names.exp.tcl
...

Tested on aarch64-linux and x86_64-linux.