rrdtool @1.8.0: cc1: error: unrecognized command line option "-fstack-protector-strong"

[ryandesign (Ryan Carsten Schmidt)]

​https://build.macports.org/builders/ports-10.6_i386-builder/builds/100329/steps/install-port/logs/stdio

/usr/bin/cc -c  -I/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_net_rrdtool/rrdtool/work/rrdtool-1.8.0/src -I/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_net_rrdtool/rrdtool/work/rrdtool-1.8.0/src -fno-common -DPERL_DARWIN -pipe -Os -fno-strict-aliasing -fstack-protector-strong -I/opt/local/include -DPERL_USE_SAFE_PUTENV -O3   -DVERSION=\"1.8\" -DXS_VERSION=\"1.8\"  "-I/opt/local/lib/perl5/5.34/darwin-thread-multi-2level/CORE"  -DPERLPATCHLEVEL=34 RRDs.c
cc1: error: unrecognized command line option "-fstack-protector-strong"

The wrong compiler (/usr/bin/cc) is being used; it doesn't understand the -fstack-protector-strong flag, whereas I suspect the compiler it should be using (/opt/local/bin/clang-mp-11) does.