tar: fix --exclude-vcs-ignores memory

tar: fix --exclude-vcs-ignores memory

The function frees the patterns' wordsplit structure without asking
add_exclude to reallocate the strings.  In many cases, this leads to
each file name in the directory being checked against the memory
location where it just got reallocated.
* src/exclist.c: Use EXCLUDE_ALLOC.
Copyright-paperwork-exempt: Yes