Description:
------------
https://www.php.net/manual/en/mbstring.installation.php

> Oniguruma is necessary for the regular expression functions with multibyte character support. Oniguruma is bundled with mbstring. As of PHP 5.4.0, if Oniguruma is already installed on the system, --with-onig[=DIR] can be specified to use the installed library. As of PHP 7.4.0 --with-onig has been removed and pkg-config is now used to detect the libonig library.

In PHP 7.3.16, I see this directory, which contains the oniguruma source: php-7.3.16/ext/mbstring/oniguruma

This file is not present in PHP 7.4.

On the same machine, PHP 7.3.16 compiled and installed correctly:

/opt/duo/third-party/php-7.3.16 # php -i | grep oniguruma
oniguruma version => 6.9.4
Multibyte regex (oniguruma) backtrack check => On

With PHP 7.4.11, this error is produced:

checking whether to enable multibyte string support... yes
checking whether to enable multibyte regex support (requires oniguruma)... yes
checking for oniguruma... no
configure: error: Package requirements (oniguruma) were not met:

Package 'oniguruma', required by 'virtual:world', not found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables ONIG_CFLAGS
and ONIG_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.
make: *** [Makefile.duo:15: Makefile] Error 1
Multibyte regex (oniguruma) version => 6.9.4

Expected result:
----------------
/opt/duo/third-party/php-7.3.16 # php -i | grep oniguruma
oniguruma version => 6.9.4
Multibyte regex (oniguruma) backtrack check => On


Actual result:
--------------
checking whether to enable multibyte string support... yes
checking whether to enable multibyte regex support (requires oniguruma)... yes
checking for oniguruma... no
configure: error: Package requirements (oniguruma) were not met:

Package 'oniguruma', required by 'virtual:world', not found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables ONIG_CFLAGS
and ONIG_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.
make: *** [Makefile.duo:15: Makefile] Error 1