pkg/56377: Inconsistent libarchive.pc for builtin libarchive

[triaxx%netbsd.org@localhost]

>Number:         56377
>Category:       pkg
>Synopsis:       Inconsistent libarchive.pc for builtin libarchive
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Aug 28 06:00:00 +0000 2021
>Originator:     Frédéric Fauberteau
>Release:        NetBSD 9.2
>Organization:
>Environment:
System: NetBSD ultralisk.triaxx.org 9.2 NetBSD 9.2 (GENERIC) #0: Wed May 12 13:15:55 UTC 2021  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
Pkgsrc: HEAD
>Description:
For packages that includes archivers/libarchive/buildlink3.mk, bmake patch && bmake configure produces an inconsistent work/.buildlink/lib/pkgconfig/libarchive.pc where the field 'Version' is not computed:
prefix=/usr
exec_prefix=/usr
libdir=/usr/lib
includedir=/usr/include

Name: libarchive
Description: library that can create and read several streaming archive formats
Version: 
Cflags: -I${includedir}
Cflags.private: -DLIBARCHIVE_STATIC
Libs: -L${libdir} -larchive
Libs.private: -llzma -lbz2 -lz

But when bmake configure is directly run, the filed 'Version' is correct:
prefix=/usr
exec_prefix=/usr
libdir=/usr/lib
includedir=/usr/include

Name: libarchive
Description: library that can create and read several streaming archive formats
Version: 3.4.0
Cflags: -I${includedir}
Cflags.private: -DLIBARCHIVE_STATIC
Libs: -L${libdir} -larchive
Libs.private: -llzma -lbz2 -lz

It occurs for builtin libarchive.
It is problematic for the development of at least audio/ardour for which the configure step checks the version of libarchive using the pkgconfig tool. When we work at patching this package, 'bmake patch' following by 'bmake build' fails for some seemingly inconsistent reason.
The same behavior can be observed for misc/rpm but without impact on the build process since the libarchive version is not tested by pkgconfig.
>How-To-Repeat:
cd /usr/pkgsrc/audio/ardour && bmake patch && bmake configure
>Fix: