The memmove() function is C99 standard function [1] and check was left for
the PCRE2 bundled library. It can be simplified by passing the compile
option instead of checking always available function on current systems.
External PCRE2 library on the system doesn't need this.
[1]: https://port70.net/~nsz/c/c99/n1256.html#7.21.2.2
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