Module/_scproxy.c compiles cleanly with clang 10.0.0 and fails with GNU gcc 8.3.0. Below is the relevant compiler error:

building '_scproxy' extension
gcc-8 -Wno-unused-result -Wsign-compare -g -Og -Wall -pipe -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Werror=implicit-function-declaration -I../cpython/Include/internal -I../cpython/Include -IObjects -IPython -I. -I/usr/local/opt/zlib/include -I/usr/local/opt/sqlite/include -I/usr/local/Cellar/ossp-uuid/1.6.2_2/include -I/usr/local/include -I/Users/jeff/sandbox/src/python3.7/cpython/Include -I/Users/jeff/sandbox/src/python3.7/build -c /Users/jeff/sandbox/src/python3.7/cpython/Modules/_scproxy.c -o build/temp.macosx-10.14-x86_64-3.8-pydebug/Users/jeff/sandbox/src/python3.7/cpython/Modules/_scproxy.o
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks/Security.framework/Headers/AuthSession.h:32,
                 from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks/Security.framework/Headers/Security.h:42,
                 from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks/SystemConfiguration.framework/Headers/SCPreferences.h:35,
                 from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks/SystemConfiguration.framework/Headers/SystemConfiguration.h:126,
                 from /Users/jeff/sandbox/src/python3.7/cpython/Modules/_scproxy.c:6:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/System/Library/Frameworks/Security.framework/Headers/Authorization.h:193:7:error: variably modified 'bytes' at file scope
  char bytes[kAuthorizationExternalFormLength];
       ^~~~~
building 'zlib' extension