[gdb/contrib] Handle STRIP_ARGS_{STRIP,KEEP}_DEBUG in cc-with-tweaks.sh

Handle new environment variable STRIP_ARGS_STRIP_DEBUG, defaulting to
--strip-debug in gdb/contrib/cc-with-tweaks.sh, such that we can easily
reproduce the PR29277 assert using:
...
$ export STRIP_ARGS_STRIP_DEBUG=--strip-all
$ make check RUNTESTFLAGS="gdb.base/jit-reader.exp \
    --target_board cc-with-gnu-debuglink"
...

For completeness sake and to avoid confusion about which of the two used strip
invocations the passed args apply to, likewise add STRIP_ARGS_KEEP_DEBUG,
defaulting to --only-keep-debug.

Script checked with shellcheck, no new warnings added.

Tested on x86_64-linux.

gdb/contrib/cc-with-tweaks.sh

@@ -74,6 +74,11 @@ READELF=${READELF:-readelf}
 DWZ=${DWZ:-dwz}
 DWP=${DWP:-dwp}
 
+# shellcheck disable=SC2206 # Allow word splitting.
+STRIP_ARGS_STRIP_DEBUG=(${STRIP_ARGS_STRIP_DEBUG:---strip-debug})
+# shellcheck disable=SC2206 # Allow word splitting.
+STRIP_ARGS_KEEP_DEBUG=(${STRIP_ARGS_KEEP_DEBUG:---only-keep-debug})
+
 have_link=unknown
 next_is_output_file=no
 output_file=a.out
@@ -267,11 +272,11 @@ if [ "$want_gnu_debuglink" = true ]; then
     debug_file="$tmpdir"/$(basename "$output_file").debug
 
     # Create stripped and debug versions of output_file.
-    strip --strip-debug "${output_file}" \
+    strip "${STRIP_ARGS_STRIP_DEBUG[@]}" "${output_file}" \
 	  -o "${stripped_file}"
     rc=$?
     [ $rc != 0 ] && exit $rc
-    strip --only-keep-debug "${output_file}" \
+    strip "${STRIP_ARGS_KEEP_DEBUG[@]}" "${output_file}" \
 	  -o "${debug_file}"
     rc=$?
     [ $rc != 0 ] && exit $rc