https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78251
--- Comment #2 from Jack Howarth <howarth.at.gcc at gmail dot com> --- It appears that config/iconv.m4 needs to be reworked for its tests to succeed. Removing INCICONV from CPPFLAGS on darwin causes the headers from /usr/include to be accidentally used against the libs from /opt/local/lib... configure:10761: /usr/bin/clang++ -arch x86_64 -std=gnu++98 -o conftest -g -Wl,-no_pie conftest.cpp -L/opt/local/lib -liconv >&5 fails because -I/opt/local/include was dropped. This should be available to configure already from... --with-libiconv-prefix[=DIR] without resorting to CPPFLAGS to pass it around to the Makefile.
