maint: simplify some syntax check exemptions

maint: simplify some syntax check exemptions

Commit 5028160 accidentally weakened the strtol prohibitions to
skip ALL files under src/util instead of the former situation of
just protecting util/virsexpr.c; even though NONE of the files
in that directory need any protection.

Shorten some long lines while at it.

* cfg.mk (exclude_file_name_regexp--sc_prohibit_strtol): No need
to exclude all of util.
(exclude_file_name_regexp--sc_prohibit_sprintf): Reduce long line.
(exclude_file_name_regexp--sc_prohibit_raw_allocation): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>