Don't clobber toolchain defaults.

https://bugs.gentoo.org/895530
--- a/configure
+++ b/configure
@@ -1381,7 +1381,7 @@ fi
 echo "Checking for secure compile option support in $CC ..."
 GCCSEC="no"
 LDSEC="no"
-GCCSECOPT="-fstack-protector-all --param ssp-buffer-size=4 -D_FORTIFY_SOURCE=2"
+GCCSECOPT="-fstack-protector-all --param ssp-buffer-size=4"
 echo '#include <stdio.h>' > $TMPC.c
 echo 'int main() { printf(""); return 0; }' >> $TMPC.c
 $CC -pie -fPIE $GCCSEPOPT -o $TMPC $TMPC.c > /dev/null 2> $TMPC.c.err