SDK version mismatch in gcc-devel

[aivazis (Michael Aivazis)]

the gcc/g++ that come with gcc-devel are unable to find the system headers due to a mismatch in the name of the SDK:

~/tmp/c++>gcc -v -v -v str.c -o str Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/opt/local/libexec/gcc/arm64-apple-darwin20/11.0.0/lto-wrapper Target: arm64-apple-darwin20 Configured with: /opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_lang_gcc-devel/gcc-devel/work/gcc-darwin-arm64-f335f738078a35dd48a0aaacbe58a0b7b11c86ce/configure --prefix=/opt/local --build=arm64-apple-darwin20 --enable-languages=c,c++,objc,obj-c++,lto,fortran,jit --libdir=/opt/local/lib/gcc-devel --includedir=/opt/local/include/gcc-devel --infodir=/opt/local/share/info --mandir=/opt/local/share/man --datarootdir=/opt/local/share/gcc-devel --with-local-prefix=/opt/local --with-system-zlib --disable-nls --program-suffix=-mp-devel --with-gxx-include-dir=/opt/local/include/gcc-devel/c++/ --with-gmp=/opt/local --with-mpfr=/opt/local --with-mpc=/opt/local --with-isl=/opt/local --enable-stage1-checking --disable-multilib --enable-lto --enable-libstdcxx-time --with-build-config=bootstrap-debug --with-as=/opt/local/bin/as --with-ld=/opt/local/bin/ld --with-ar=/opt/local/bin/ar --with-bugurl=​https://trac.macports.org/newticket --enable-host-shared --disable-tls --with-pkgversion='MacPorts gcc-devel 11-20201205_0' --with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX11.0.sdk

but

~/tmp/c++>ls /Library/Developer/CommandLineTools/SDKs/MacOSX MacOSX.sdk/ MacOSX10.15.sdk/ MacOSX11.1.sdk/