I've written patch which builds mawk with external regexp engine.
There are lots of different regexp engines world-wide.
You can use any of them
On most modern systems system-wide regexp engine also conforms to POSIX.
As a result mawk conforms to POSIX regexp, if you build
it with appropriate regexp engine like this.
# regexec/regcomp functions from libc will be used
./configure && make
# TRE implementation will be used
CFLAGS='-O3 -I/usr/include/tre' LDFLAGS='-ltre' ./configure && make
Whether UTF-8 support is provided or not
also depends on external regexp library.
If you find bugs in it, let me know.
The patch is here.
http://www.mova.org/~cheusov/pub/mawk_external_regexp.patch
--
Best regards, Aleksey Cheusov.
AC> I've written patch which builds mawk with external regexp engine.
[skipped]
Do not forger to run autoconf before configuring mawk.
autoconf2.13 work fine.