Builtin iconv not found on Darwin 21.6.0

[Frédéric Fauberteau <triaxx%NetBSD.org@localhost>]

I got an error when configuring php81-iconv on Darwin 21.6.0:

===> Configuring for php81-iconv-8.1.10
[…]
checking for iconv support... yes, shared
configure: error: Please specify the install prefix of iconv with --with-iconv=<DIR>

I observe these values:
% bmake show-var VARNAME=CHECK_BUILTIN.iconv
no
% bmake show-var VARNAME=USE_BUILTIN.iconv
yes
% bmake show-var VARNAME=BUILTIN_LIB_FOUND.iconv
yes

As result of searching libiconv in libraries (among others):
% find /Library -name "*iconv*"
/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/include/iconv.h
/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/lib/libiconv.2.4.0.tbd
/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/lib/libiconv.2.tbd
/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/lib/libiconv.tbd

I think maybe BUILDINK_FIND_LIBS is misled by the tbd files…

I can fix it with this patch:
Index: platform/Darwin.mk
===================================================================
RCS file: /cvsroot/pkgsrc/mk/platform/Darwin.mk,v
retrieving revision 1.117
diff -r1.117 Darwin.mk
211a212,214
> .if ${OPSYS_VERSION} >= 210600
> _OPSYS_PREFER.iconv?=         pkgsrc
> .endif

I made the hypothesis that it was no problem before 21.6.0. Actually,I have doubts that it is the right solution since I don’t know the Mac system.