common.mak: use '--' for rm calls to distinguish between options and files
common.mak: use '--' for rm calls to distinguish between options and files

Use '--' for rm calls to distinguish between options and files. This
fixes, for example, the following error:

make[1]: Entering directory '/root/git/s390-tools/genprotimg/src'
rm -f *.gcda *.gcno *.gcov
rm: invalid option -- '.'
Try 'rm ./-.gcno' to remove the file '-.gcno'.
Try 'rm --help' for more information.
make[1]: *** [../../common.mak:369: clean_gcov] Error 1

Acked-by: Jan Höppner <96138615ab4af0813785fa10d283f3d37eca3b78@linux.ibm.com>
Signed-off-by: Marc Hartmayer <7bafc8cd4e6394916d396e4f8cde69753be8d066@linux.ibm.com>
Signed-off-by: Jan Höppner <96138615ab4af0813785fa10d283f3d37eca3b78@linux.ibm.com>

ibm-s390-tools/s390-tools,ibm-s390-tools/s390-tools,ibm-s390-tools/s390-tools,ibm-s390-tools/s390-tools