cc is not found during AWK bootstrapping on OpenMPTCProuter

[sskras]

After working around the #132 issue the boostrapping aborts on OpenMPTCProuter v0.59.1-5.4:

root@OpenMPTCProuter:~/debug/src/github.com/NetBSD/pkgsrc.git# rm -rf work/; time bootstrap/bootstrap
  ...
===> Bootstrapping awk
===> running: /bin/sh /root/debug/src/github.com/NetBSD/pkgsrc.git/work/bin/install-sh -d -o root -g root /root/debug/src/github.com/NetBSD/pkgsrc.git/work/awk
===> running: (cd /root/debug/src/github.com/NetBSD/pkgsrc.git/work/awk && /root/debug/src/github.com/NetBSD/pkgsrc.git/work/bin/bmake  -j1 -f Makefile CC="cc" CFLAGS="")
cc   -c awkgram.tab.c
sh: cc: not found
*** [awkgram.tab.o] Error code 127

bmake: stopped in /root/debug/src/github.com/NetBSD/pkgsrc.git/work/awk
1 error

bmake: stopped in /root/debug/src/github.com/NetBSD/pkgsrc.git/work/awk
===> exited with status 2
aborted.

real    0m12.492s
user    0m8.287s
sys     0m0.901s

Full output from the terminal: 08-cc-is-not-found-during-AWK-bootstrap-on-OpenMPTCProuter.log

[sskras]

It can be worked around by CC=gcc; export CC.

Why is this needed? Looks like a bug to me.