[scudo] Add reallocarray C wrapper. (#183385)
`reallocarray()` is a POSIX extension to C standard which wraps
`realloc` function and adds `calloc`-like overflow detection. It is
available in glibc and some other standard library implementations. Add
`reallocarray` to the list of Scudo C wrappers, so that the code that
depends on `reallocarray` presence will continue to work.
