Debian is apparently offended that pcre2-posix implements POSIX API,
thus it renames all posix-compatible symbols in libpcre2-posix to have the
PCRE2 prefix. But Debian doesn't do anything to pcre2posix.h header,
so any unaware application will get POSIX compatible type names
and function prototypes from pcre2, but actual symbols will come
from libc.
To remedy this enormous incongruity we have to redefine POSIX-compatible
function names in pcre2posix to match Debian's hack.