BIND 9.18 fails to configure on NetBSD

Summary

BIND 9.18.8 fails to configure on NetBSD (-current or 9.3).

BIND version used

Source code for 9.18.8.

Steps to reproduce

./configure --with-libxml2=yes --with-tuning=large --sysconfdir=/etc --localstatedir=/var

What is the current bug behavior?

The above configure line fails with

checking for jemalloc/jemalloc.h... no
configure: WARNING: jemalloc not found; performance will be reduced
configure: error: You cannot compile without jemalloc; jemalloc is the system allocator on NetBSD

and config.log contains

configure:24692: result: no
configure:24692: checking jemalloc/jemalloc.h presence
configure:24692: gcc -E  conftest.c
conftest.c:143:10: fatal error: jemalloc/jemalloc.h: No such file or directory
  143 | #include <jemalloc/jemalloc.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.
configure:24692: $? = 1

and

configure:24692: result: no
configure:24692: checking for jemalloc/jemalloc.h
configure:24692: result: no
configure:24873: WARNING: jemalloc not found; performance will be reduced
configure:24888: error: You cannot compile without jemalloc; jemalloc is the system allocator on NetBSD

Trying the above configure line with --with-jemalloc=yes doesn't really change this, I still get

checking for jemalloc/jemalloc.h... no
configure: error: jemalloc not found

Trying the above configure line with --with-jemalloc=no also doesn't succeed, then I get:

configure: error: You cannot compile without jemalloc; jemalloc is the system allocator on NetBSD

What is the expected correct behavior?

While some of the text above is correct, i.e. that the system malloc() implementation on NetBSD is based on jemalloc, NetBSD does not ship with a header accessible as <jemalloc/jemalloc.h>. I do see our man page for jemalloc(3) does (incorrectly) mention that include file location in its SYNOPSIS, that's a separate (NetBSD) documentation bug.

It does however seem that BIND's configure script still insists on the presence of this header. Not sure what FreeBSD does, looking at configure.ac if it doesn't have <jemalloc/jemalloc.h> either, it will be similarly affected.

Relevant configuration files

N/A

Relevant logs and/or screenshots

See above.

Possible fixes

So far this points towards configure.ac. Not sure if there is also actual code which insists on <jemalloc/jemalloc.h>. One hurdle at a time...

...

It seems lib/isc/mem.c is the only other file which (conditionally) wants this header.