[gdb/contrib] Use temp dir for gdb-add-index in cc-with-tweaks.sh

When running test-case gdb.dwarf2/gdb-index.exp cleanly by issuing this
command:
...
$ rm -Rf build/gdb/testsuite/outputs/gdb.dwarf2/gdb-index
...
before running, it passes both with native and target board
cc-with-gdb-index.

But when we run the test-case first with native and then with
cc-with-gdb-index without intermediate cleanup, we get instead:
...
 Running src/gdb/testsuite/gdb.dwarf2/gdb-index.exp ...
 gdb compile failed, cc-with-tweaks.sh: Index file \
   build/gdb/testsuite/outputs/gdb.dwarf2/gdb-index/gdb-index.gdb-index \
   exists, won't clobber.

                 === gdb Summary ===

 # of untested testcases         1
...

What happens is that the native run produces a file
build/gdb/testsuite/outputs/gdb.dwarf2/gdb-index/gdb-index.gdb-index, which
causes gdb/contrib/cc-with-tweaks.sh to hit this code:
...
index_file="${output_file}.gdb-index"
if [ "$want_index" = true ] && [ -f "$index_file" ]
then
    echo "$myname: Index file $index_file exists, won't clobber." >&2
    exit 1
fi
...

The gdb-add-index script has a problem that it uses temp files alongside the
executable, filed as PR25843.

The code in cc-with-tweaks.sh attempts to detect the case that creating such a
temp file would overwrite an pre-existing file.  It however does this only for
a single file, while gdb-add-index uses more temporary files:
- <exec>.gdb-index
- <exec>.debug_names
- <exec>.debug_str
- <exec>.debug_str.merge
- <exec>.debug_str.err

Fix this by working around PR25843 in a more generic way:
- move the executable into a temp directory
- execute gdb-add-index, allowing it to create any temp file alongside the
  executable in the temp directory
- move the executable back to the original location

Tested on x86_64-linux, with target board cc-with-debug-index.

gdb/ChangeLog:

2020-04-24  Tom de Vries  <tdevries@suse.de>

	* contrib/cc-with-tweaks.sh: Remove <exec>.gdb-index file handling.
	Run gdb-add-index inside temp dir.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2020-04-24  Tom de Vries  <tdevries@suse.de>
+
+	* contrib/cc-with-tweaks.sh: Remove <exec>.gdb-index file handling.
+	Run gdb-add-index inside temp dir.
+
 2020-04-23  Tom Tromey  <tromey@adacore.com>
 
 	* windows-tdep.c (is_linked_with_cygwin_dll): Always update "iter"

gdb/contrib/cc-with-tweaks.sh

@@ -144,13 +144,6 @@ then
     exit $?
 fi
 
-index_file="${output_file}.gdb-index"
-if [ "$want_index" = true ] && [ -f "$index_file" ]
-then
-    echo "$myname: Index file $index_file exists, won't clobber." >&2
-    exit 1
-fi
-
 output_dir="${output_file%/*}"
 [ "$output_dir" = "$output_file" ] && output_dir="."
 
@@ -176,12 +169,16 @@ if [ "$want_objcopy_compress" = true ]; then
 fi
 
 if [ "$want_index" = true ]; then
+    get_tmpdir
+    mv "$output_file" "$tmpdir"
+    tmpfile="$tmpdir/$(basename $output_file)"
     # Filter out these messages which would stop dejagnu testcase run:
     # echo "$myname: No index was created for $file" 1>&2
     # echo "$myname: [Was there no debuginfo? Was there already an index?]" 1>&2
-    GDB=$GDB $GDB_ADD_INDEX $index_options "$output_file" 2>&1 \
+    GDB=$GDB $GDB_ADD_INDEX $index_options "$tmpfile" 2>&1 \
 	| grep -v "^${GDB_ADD_INDEX##*/}: " >&2
     rc=${PIPESTATUS[0]}
+    mv "$tmpfile" "$output_file"
     [ $rc != 0 ] && exit $rc
 fi
 
@@ -237,5 +234,4 @@ if [ "$want_dwp" = true ]; then
     fi
 fi
 
-rm -f "$index_file"
 exit $rc