I'm trying once again to get the test suite up to snuff on Cygwin so I can start running a buildbot (particularly now that PEP 539 is done).  However, as of issue28180 the build fails with:

gcc    -o python.exe Programs/python.o libpython3.7m.dll.a -lintl -ldl    -lm
Programs/python.o: In function `main':
./Programs/python.c:81: undefined reference to `_Py_LegacyLocaleDetected'
./Programs/python.c:81:(.text.startup+0x86): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `_Py_LegacyLocaleDetected'
./Programs/python.c:82: undefined reference to `_Py_CoerceLegacyLocale'
./Programs/python.c:82:(.text.startup+0x19f): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `_Py_CoerceLegacyLocale'
collect2: error: ld returned 1 exit status

It seems _Py_LegacyLocaleDetected and _PyCoerceLegacyLocale are missing the necessary PyAPI_FUNC declarations in pylifecycle.h.