pkg/54983: devel/libevent cannot write .pc file in builtin mode

[triaxx%netbsd.org@localhost]

>Number:         54983
>Category:       pkg
>Synopsis:       devel/libevent cannot write .pc file in builtin mode
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Feb 19 04:25:00 +0000 2020
>Originator:     Frédéric Fauberteau
>Release:        NetBSD 8.0
>Organization:
>Environment:
System: NetBSD hydralisk.triaxx.org 8.0 NetBSD 8.0 (GENERIC) #0: Fri Jan 17 23:04:35 CET 2020  triaxx%hydralisk.triaxx.org@localhost:/mnt/ccd0/sysbuild/hydralisk-8.0/amd64/obj/mnt/ccd0/netbsd/netbsd-8-0-RELEASE/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
The issue occurs only when I run a pbulk in a sandbox. When I build packages that depend on devel/libevent (and I don't declare any preference for pkgsrc), I get the following error in the configure step. Here is an example with mail/rspamd:
=> Generating pkg-config files for builtin libevent package.
set -e;						 /bin/mkdir -p /var/pkgsrc/work/mail/rspamd/work/.buildlink/lib/pkgconfig;			 ls -al /var/pkgsrc;				 ls -al /var/pkgsrc/work;			 ls -al /var/pkgsrc/work/mail/rspamd/work;	 ls -al /var/pkgsrc/work/mail/rspamd/work/.buildlink/lib/pkgconfig;			 {						 echo "prefix=";		 echo "exec_prefix=\${prefix}";		 echo "libdir=\${exec_prefix}/lib";		 echo "includedir=\${prefix}/include";	 echo "";					 echo "Name: libevent";			 echo "Description: libevent is an asynchronous notification event loop library";  echo "Version: 1.4.4";	 echo "Libs: -Wl,-R\${libdir} -L\${libdir} -levent";	 echo "Cflags: -I\${includedir}";		 } >> /var/pkgsrc/work/mail/rspamd/work/.buildlink/lib/pkgconfig/libevent.pc;
sh: cannot create /var/pkgsrc/work/mail/rspamd/work/.buildlink/lib/pkgconfig/libevent.pc: permission denied
*** Error code 2

I added a 'ls -al ${BLKDIR_PKGCFG};' to inspect the permissions but I don't see any problem:
drwxr-xr-x  2 pbulk  wheel  1024 Feb 18 18:12 .
drwxr-xr-x  4 pbulk  wheel  4096 Feb 18 18:12 ..
lrwxr-xr-x  1 pbulk  wheel    30 Feb 18 18:12 fann.pc -> /usr/pkg/lib/pkgconfig/fann.pc
lrwxr-xr-x  1 pbulk  wheel    33 Feb 18 18:12 gio-2.0.pc -> /usr/pkg/lib/pkgconfig/gio-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    38 Feb 18 18:12 gio-unix-2.0.pc -> /usr/pkg/lib/pkgconfig/gio-unix-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    34 Feb 18 18:12 glib-2.0.pc -> /usr/pkg/lib/pkgconfig/glib-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    35 Feb 18 18:12 gmime-2.6.pc -> /usr/pkg/lib/pkgconfig/gmime-2.6.pc
lrwxr-xr-x  1 pbulk  wheel    37 Feb 18 18:12 gmodule-2.0.pc -> /usr/pkg/lib/pkgconfig/gmodule-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    44 Feb 18 18:12 gmodule-export-2.0.pc -> /usr/pkg/lib/pkgconfig/gmodule-export-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    47 Feb 18 18:12 gmodule-no-export-2.0.pc -> /usr/pkg/lib/pkgconfig/gmodule-no-export-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    37 Feb 18 18:12 gobject-2.0.pc -> /usr/pkg/lib/pkgconfig/gobject-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    35 Feb 18 18:12 gpg-error.pc -> /usr/pkg/lib/pkgconfig/gpg-error.pc
lrwxr-xr-x  1 pbulk  wheel    36 Feb 18 18:12 gpgme-glib.pc -> /usr/pkg/lib/pkgconfig/gpgme-glib.pc
lrwxr-xr-x  1 pbulk  wheel    31 Feb 18 18:12 gpgme.pc -> /usr/pkg/lib/pkgconfig/gpgme.pc
lrwxr-xr-x  1 pbulk  wheel    37 Feb 18 18:12 gthread-2.0.pc -> /usr/pkg/lib/pkgconfig/gthread-2.0.pc
lrwxr-xr-x  1 pbulk  wheel    33 Feb 18 18:12 hiredis.pc -> /usr/pkg/lib/pkgconfig/hiredis.pc
lrwxr-xr-x  1 pbulk  wheel    34 Feb 18 18:12 icu-i18n.pc -> /usr/pkg/lib/pkgconfig/icu-i18n.pc
lrwxr-xr-x  1 pbulk  wheel    32 Feb 18 18:12 icu-io.pc -> /usr/pkg/lib/pkgconfig/icu-io.pc
lrwxr-xr-x  1 pbulk  wheel    32 Feb 18 18:12 icu-uc.pc -> /usr/pkg/lib/pkgconfig/icu-uc.pc
lrwxr-xr-x  1 pbulk  wheel    35 Feb 18 18:12 libassuan.pc -> /usr/pkg/lib/pkgconfig/libassuan.pc
lrwxr-xr-x  1 pbulk  wheel    35 Feb 18 18:12 libcrypto.pc -> /usr/pkg/lib/pkgconfig/libcrypto.pc
lrwxr-xr-x  1 pbulk  wheel    34 Feb 18 18:12 libevent.pc -> /usr/pkg/lib/pkgconfig/libevent.pc
lrwxr-xr-x  1 pbulk  wheel    39 Feb 18 18:12 libevent_core.pc -> /usr/pkg/lib/pkgconfig/libevent_core.pc
lrwxr-xr-x  1 pbulk  wheel    40 Feb 18 18:12 libevent_extra.pc -> /usr/pkg/lib/pkgconfig/libevent_extra.pc
lrwxr-xr-x  1 pbulk  wheel    42 Feb 18 18:12 libevent_openssl.pc -> /usr/pkg/lib/pkgconfig/libevent_openssl.pc
lrwxr-xr-x  1 pbulk  wheel    43 Feb 18 18:12 libevent_pthreads.pc -> /usr/pkg/lib/pkgconfig/libevent_pthreads.pc
lrwxr-xr-x  1 pbulk  wheel    32 Feb 18 18:12 libffi.pc -> /usr/pkg/lib/pkgconfig/libffi.pc
lrwxr-xr-x  1 pbulk  wheel    33 Feb 18 18:12 libpcre.pc -> /usr/pkg/lib/pkgconfig/libpcre.pc
lrwxr-xr-x  1 pbulk  wheel    35 Feb 18 18:12 libpcre16.pc -> /usr/pkg/lib/pkgconfig/libpcre16.pc
lrwxr-xr-x  1 pbulk  wheel    36 Feb 18 18:12 libpcrecpp.pc -> /usr/pkg/lib/pkgconfig/libpcrecpp.pc
lrwxr-xr-x  1 pbulk  wheel    38 Feb 18 18:12 libpcreposix.pc -> /usr/pkg/lib/pkgconfig/libpcreposix.pc
lrwxr-xr-x  1 pbulk  wheel    35 Feb 18 18:12 libsodium.pc -> /usr/pkg/lib/pkgconfig/libsodium.pc
lrwxr-xr-x  1 pbulk  wheel    32 Feb 18 18:12 libssl.pc -> /usr/pkg/lib/pkgconfig/libssl.pc
lrwxr-xr-x  1 pbulk  wheel    33 Feb 18 18:12 lua-5.3.pc -> /usr/pkg/lib/pkgconfig/lua-5.3.pc
lrwxr-xr-x  1 pbulk  wheel    69 Feb 18 18:12 lua.pc -> /var/pkgsrc/work/mail/rspamd/work/.buildlink/lib/pkgconfig/lua-5.3.pc
lrwxr-xr-x  1 pbulk  wheel    33 Feb 18 18:12 openssl.pc -> /usr/pkg/lib/pkgconfig/openssl.pc
lrwxr-xr-x  1 pbulk  wheel    29 Feb 18 18:12 sqlite3.pc -> /usr/lib/pkgconfig/sqlite3.pc
lrwxr-xr-x  1 pbulk  wheel    26 Feb 18 18:12 zlib.pc -> /usr/lib/pkgconfig/zlib.pc

I cannot reproduce the problem manually even in the chrooted sandbox.
>How-To-Repeat:
By trying to build mail/spamd in a sandboxed pbulk with builtin devel/libevent.
>Fix: