> Here's the output I get for NetBSD-i386-3.99.21:
...
> cc -c -I.  -fno-strict-aliasing -pipe -Wdeclaration-after-statement -O2
> -I/usr/pkg/include -I/usr/include -DHAVE_CTYPE_H -DHAVE_STDLIB_H
> -DHAVE_STRING_H -I/usr/pkg/include -I/usr/include -DVERSION=\"1.0\"
> -DXS_VERSION=\"1.0\" -DPIC -fPIC
> "-I/usr/pkg/lib/perl5/5.8.0/i386-netbsd-thread-multi/CORE"  lib_dewey.c

It does have the CPPFLAGS here, but not for me.

...
> => Unwrapping files-to-be-installed.
$ make
===> Skipping vulnerability checks.
WARNING: No /opt/rainier/pkgsrc/distfiles/pkg-vulnerabilities file found.
WARNING: To fix, install the pkgsrc/security/audit-packages
WARNING: package and run: ``/usr/pkg/sbin/download-vulnerability-list''.
work.glacier -> 
/home/packages/tmp-pkgsrc/pkgtools/p5-pkgsrc-Dewey/work.glacier
===> Installing dependencies for p5-pkgsrc-Dewey-1.0nb1
=> Required installed package perl>=5.8.7: perl-5.8.7nb4 found
===> Overriding tools for p5-pkgsrc-Dewey-1.0nb1
===> Creating toolchain wrappers for p5-pkgsrc-Dewey-1.0nb1
===> Extracting for p5-pkgsrc-Dewey-1.0nb1
/bin/mkdir -p 
/home/packages/tmp-pkgsrc/pkgtools/p5-pkgsrc-Dewey/work.glacier/p5-pkgsrc-Dewey-1.0
/bin/cp -r /opt/rainier/pkgsrc/pkgtools/p5-pkgsrc-Dewey/files/* 
/home/packages/tmp-pkgsrc/pkgtools/p5-pkgsrc-Dewey/work.glacier/p5-pkgsrc-Dewey-1.0
for f in lib/dewey.c lib/dewey.h lib/defs.h; do  /bin/cp 
../../pkgtools/pkg_install/files/$f 
/home/packages/tmp-pkgsrc/pkgtools/p5-pkgsrc-Dewey/work.glacier/p5-pkgsrc-Dewey-1.0;  
done
/bin/mv 
/home/packages/tmp-pkgsrc/pkgtools/p5-pkgsrc-Dewey/work.glacier/p5-pkgsrc-Dewey-1.0/dewey.c 
/home/packages/tmp-pkgsrc/pkgtools/p5-pkgsrc-Dewey/work.glacier/p5-pkgsrc-Dewey-1.0/lib_dewey.c
/usr/bin/touch 
/home/packages/tmp-pkgsrc/pkgtools/p5-pkgsrc-Dewey/work.glacier/p5-pkgsrc-Dewey-1.0/nbcompat.h
===> Patching for p5-pkgsrc-Dewey-1.0nb1
===> Configuring for p5-pkgsrc-Dewey-1.0nb1
Checking if your kit is complete...
Looks good
Writing Makefile for pkgsrc::Dewey
===> Building for p5-pkgsrc-Dewey-1.0nb1
cp Dewey.pm blib/lib/pkgsrc/Dewey.pm
AutoSplitting blib/lib/pkgsrc/Dewey.pm (blib/lib/auto/pkgsrc/Dewey)
/usr/pkg/bin/perl /usr/pkg/lib/perl5/5.8.0/ExtUtils/xsubpp  -typemap 
/usr/pkg/lib/perl5/5.8.0/ExtUtils/typemap -typemap typemap  Dewey.xs > 
Dewey.xsc && mv Dewey.xsc Dewey.c
cc -c  -I.  -fno-strict-aliasing -pipe -I/usr/pkg/include -O2 -pthread 
-I/usr/include    -DVERSION=\"1.0\"  -DXS_VERSION=\"1.0\" -DPIC -fPIC 
"-I/usr/pkg/lib/perl5/5.8.0/i386-netbsd-thread-multi/CORE"   lib_dewey.c
lib_dewey.c:82: error: `NULL' undeclared here (not in a function)
lib_dewey.c:82: error: initializer element is not constant
lib_dewey.c:82: error: (near initialization for `tests[6].s')
lib_dewey.c:82: error: initializer element is not constant
lib_dewey.c:82: error: (near initialization for `tests[6]')
lib_dewey.c:93: error: `NULL' undeclared here (not in a function)
lib_dewey.c:93: error: initializer element is not constant
lib_dewey.c:93: error: (near initialization for `modifiers[7].s')
lib_dewey.c:93: error: initializer element is not constant
lib_dewey.c:93: error: (near initialization for `modifiers[7]')
lib_dewey.c: In function `mkcomponent':
lib_dewey.c:134: error: `NULL' undeclared (first use in this function)
lib_dewey.c:134: error: (Each undeclared identifier is reported only once
lib_dewey.c:134: error: for each function it appears in.)
lib_dewey.c:134: error: `EXIT_FAILURE' undeclared (first use in this 
function)
lib_dewey.c: In function `dewey_match':
lib_dewey.c:249: error: `NULL' undeclared (first use in this function)
lib_dewey.c:256: error: `size_t' undeclared (first use in this function)
*** Error code 1