Compiler problems on OS X 10.12.3, pkgsrc-2016Q4

[Louis Guillaume <louis%zabrico.com@localhost>]

Since upgrading to OS X Sierra (10.12) I've been having compiler issues 
with pkgsrc. I was hoping 2016Q4 would have a fix but it doesn't seem so.

To clean the slate, I removed all packages and re-bootstrapped, after 
updating Xcode and re-running "xcode-select --install" to make sure the 
environment was up-to-date.

Here's my bootstrap command...

PKG_SYSCONFBASE=/etc \
WRKOBJDIR=/opt/pkgobj ./bootstrap --abi 64 --compiler clang --pkgdbdir 
/opt/pkg/.dbdir --prefix /opt/pkg --sysconfdir /etc --varbase /var 
--workdir /tmp/pkgsrc-bootstrap

The bootstrap appears to have worked correctly. But packages fail to 
build like this...

===> Configuring for digest-20160304
=> Modifying GNU configure scripts to avoid --recheck
=> Replacing config-guess with pkgsrc versions
=> Replacing config-sub with pkgsrc versions
=> Replacing install-sh with pkgsrc version
checking build system type... x86_64-apple-darwin16
checking host system type... x86_64-apple-darwin16
checking whether make sets $(MAKE)... yes
checking for gawk... /usr/bin/awk
checking for x86_64-apple-darwin16-gcc... cc
checking whether the C compiler works... no
configure: error: in `/opt/pkgobj/pkgtools/digest/work/digest-20160304':
configure: error: C compiler cannot create executables
See `config.log' for more details
*** Error code 77

Stop.
bmake[1]: stopped in /usr/pkgsrc/pkgtools/digest
*** Error code 1



The only significant things I can find in mk.conf are these...

PKGSRC_COMPILER=        clang
ABI=                    64
WRKOBJDIR=/opt/pkgobj
PKG_SYSCONFBASE=/etc
DEPENDS_TARGET=package-install


... and those seem pretty benign to me.


Any idea what might be going on here? Any help would be greatly appreciated.

Louis