cmake: Configure failure with MacOS 11.1 and Xcode 12.3

[mf2k (Frank Schima)]

I'm updated to macOS 11.1 and Xcode 12.3 with the command line tools.

I'm now seeing the following build error with cmake:

:debug:configure system:  cd "/opt/local/var/macports/build/_opt_mports_macports-ports_devel_cmake/cmake/work/cmake-3.19.1" && ./bootstrap --prefix=/opt/local --docdir=share/doc/cmake --parallel=12 --init=/opt/local/var/macports/build/_opt_mports_macports-ports_devel_cmake/cmake/work/cmake-3.19.1/macports.cmake --system-libs --no-system-jsoncpp --no-system-librhash --no-qt-gui -- 
:info:configure ---------------------------------------------
:info:configure CMake 3.19.1, Copyright 2000-2020 Kitware, Inc. and Contributors
:info:configure ---------------------------------------------
:info:configure Error when bootstrapping CMake:
:info:configure Cannot find appropriate C compiler on this system.
:info:configure Please specify one using environment variable CC.
:info:configure See cmake_bootstrap.log for compilers attempted.
:info:configure ---------------------------------------------
:info:configure Log of errors: /opt/local/var/macports/build/_opt_mports_macports-ports_devel_cmake/cmake/work/cmake-3.19.1/Bootstrap.cmk/cmake_bootstrap.log

In the cmake_bootstrap.log it says:

cmake_bootstrap_64725_test.c:18:10: fatal error: 'stdio.h' file not found
#include <stdio.h>
         ^~~~~~~~~
1 error generated.
Test failed to compile

I will attach both logs.