pkg_install/libfetch build failure with clang

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I've set up a NetBSD-8 server to use clang as PKGSRC_COMPILER (more later) 
and now building pkg_install (from 2022Q2) fails to build libfetch:

#   compile  libfetch/http.o
clang -O2 -fPIC -I/usr/include  -std=gnu99     -Wno-sign-compare -Wno-pointer-sign  -Wall -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wno-sign-compare    -Wreturn-type -Wswitch -Wshadow -Wcast-qual -Wwrite-strings -Wextra -Wno-unused-parameter -Wno-sign-compare -Wsign-compare -Wformat=2  -Werror   -fPIE  -D_LARGEFILE_SOURCE -D_LARGE_FILES -D_FILE_OFFSET_BITS=64 -DDEF_UMASK=0022 -I/var/work/pkgsrc/pkgtools/pkg_install/work/libfetch -I/var/work/pkgsrc/pkgtools/pkg_install/work -DHAVE_NBCOMPAT_H=1 -I/var/work/pkgsrc/pkgtools/pkg_install/work/libnbcompat -I/usr/include -I. -D_LARGEFILE_SOURCE -D_LARGE_FILES -D_FILE_OFFSET_BITS=64 -DINET6 -DWITH_SSL -DFTP_COMBINE_CWDS  -c    http.c -o http.o
http.c:622:9: error: variable 'r' set but not used [-Werror,-Wunused-but-set-variable]
        int t, r;
               ^

Any hints?