[gdb/testsuite] Fix gdb.dwarf2/fission-relative-dwo.exp with cc-with-gdb-index

When running with target board cc-with-gdb-index, we run into:
...
gdb compile failed, warning: Could not find DWO CU \
  fission-relative-dwo.dwo(0x1234) referenced by CU at offset 0xc7 \
  [in module outputs/gdb.dwarf2/fission-relative-dwo/.tmp/fission-relative-dwo]
UNTESTED: gdb.dwarf2/fission-relative-dwo.exp: fission-relative-dwo.exp
ERROR: failed to compile fission-relative-dwo
...

The problem is that:
- the .dwo file is found relative to the executable, and
- cc-with-tweaks.sh moves the executable to a temp dir, but not
  the .dwo file.

Fix this by copying the .dwo file alongside the executable in the temp dir.

Verified changes using shellcheck.

Tested on x86_64-linux.

gdb/ChangeLog:

2021-08-02  Tom de Vries  <tdevries@suse.de>

	* contrib/cc-with-tweaks.sh: Copy .dwo files alongside executable.

gdb/contrib/cc-with-tweaks.sh

@@ -179,6 +179,19 @@ fi
 if [ "$want_index" = true ]; then
     get_tmpdir
     mv "$output_file" "$tmpdir"
+    output_dir=$(dirname "$output_file")
+
+    # Copy .dwo file alongside, to fix gdb.dwarf2/fission-relative-dwo.exp.
+    # Use copy instead of move to not break
+    # rtf=gdb.dwarf2/fission-absolute-dwo.exp.
+    dwo_pattern="$output_dir/*.dwo"
+    for f in $dwo_pattern; do
+	if [ "$f" = "$dwo_pattern" ]; then
+	    break
+	fi
+	cp "$f" "$tmpdir"
+    done
+
     tmpfile="$tmpdir/$(basename $output_file)"
     # Filter out these messages which would stop dejagnu testcase run:
     # echo "$myname: No index was created for $file" 1>&2
@@ -187,6 +200,7 @@ if [ "$want_index" = true ]; then
 	| grep -v "^${GDB_ADD_INDEX##*/}: " >&2
     rc=${PIPESTATUS[0]}
     mv "$tmpfile" "$output_file"
+    rm -f "$tmpdir"/*.dwo
     [ $rc != 0 ] && exit $rc
 fi