compat.pcre2

// compat.pcre2 — exercised the way glib's GRegex uses it.
//
// WHAT THIS ASSERTS AND WHY EACH ONE IS HERE
//
// The failures worth catching in a regex engine are not "it did not link".
// They are the ones where the library builds, links, runs, and gives a subtly
// wrong answer because a probe macro said something untrue. Each check below
// names a specific decision in the descriptor:
//
//   compile + match      the sources really were compiled, not just linked
//   \p{Han} / \X         SUPPORT_UNICODE, i.e. that pcre2_ucd.c's tables are in
//   PCRE2_UTF            that UTF-8 mode works, which is all glib ever uses
//   the character tables that pcre2_chartables.c.dist was compiled, and in the
//                        C locale — the file the descriptor does NOT let a
//                        `pcre2_dftables` run produce from the build machine
//   pcre2_config(JIT)    that JIT is OFF and SAYS so, rather than crashing
//   capture groups       pcre2_substring_*, which glib's g_match_info_fetch is

#ifdef __linux__

// ⚠️ REQUIRED BEFORE THE HEADER, and pcre2.h says so with an #error if it is
// missing. The header uses it to choose which of the three code-unit widths to
// …