If we don't know how to convert between two encodings, make sure
we error instead of ignoring the issue.

Explicitly use vtbl_pass if we are round-tripping wchar->wchar or
8bit->8bit. Fingers crossed that nothing else relies on the
vtbl_pass fallback...

mbstring can be built without mbregex support, in which case these
tests would fail.  Thus we add respective skip conditions.

_php_mb_match_regex() is supposed to return != 0 on success, and 0 on
failure.  pcre2_match() returns >= 0 on success, and < 0 on failure.
We map the result accordingly.

Since this patch fixes four failing tests, there is no need to add
another.

* PHP-7.2:
  Fix #76704: mb_detect_order return value varies based on argument type

* PHP-7.1:
  Fix #76704: mb_detect_order return value varies based on argument type

php_mb_parse_encoding_list() and php_mb_parse_encoding_array() are
supposed to return SUCCESS and FAILURE, not 1 and 0, respectively.

Autoconf 2.50 released in 2001 made several macros obsolete including
the AC_TRY_RUN, AC_TRY_COMPILE and AC_TRY_LINK:
http://git.savannah.gnu.org/cgit/autoconf.git/tree/ChangeLog.2

These macros should be replaced with the current AC_FOO_IFELSE instead:
- AC_TRY_RUN with AC_RUN_IFELSE and AC_LANG_SOURCE
- AC_TRY_LINK with AC_LINK_IFELSE and AC_LANG_PROGRAM
- AC_TRY_COMPILE with AC_COMPILE_IFELSE and AC_LANG_PROGRAM

PHP 5.4 to 7.1 require Autoconf 2.59+ version, PHP 7.2 and above require
2.64+ version, and the PHP 7.2 phpize script requires 2.59+ version which
are all greater than above mentioned 2.50 version therefore systems
should be well supported by now.

This patch was created with the help of autoupdate script:
autoupdate <file>

Reference docs:
- https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Obsolete-Macros.html
- https://www.gnu.org/software/autoconf/manual/autoconf-2.59/autoconf.pdf

PHP build system already builds necessary files also from libmbfl
directory using the mbstring config.m4 file.