11687 isaexec() leaks memory if realloc fails

This is just one place where a simple swap of realloc() for reallocf() would fix a memory leak in the case that the memory reallocation fails.
There are potentially quite a few of these in gate:

% rg -lP '\b(\S+)\s*=\s*realloc\(\1\s*,' | wc -l
     202