[SV 63821] Don't set up default suffix rules if makefile sets -r

[SV 63821] Don't set up default suffix rules if makefile sets -r

When built-in rules are disabled by adding -r to MAKEFLAGS in the
makefile, don't add suffix rules at all so that if suffixes are
added back via .SUFFIXES, the rules are still not there.

* src/main.c (main): Set default suffix rules after parsing makefiles.
* src/default.c (install_default_suffix_rules): Install a default
suffix rule only if there is no user defined rule.
* tests/scripts/features/suffixrules: Add tests.