headers: crt: split out corecrt_wstdio.h
headers: Replace extern "C" and drop #pragma pack
headers: crt: Improve _Pragma support and add helper macros
crt: Regenerate configure and Makefile.in
crt/testcases/t_global_ctors: Add DLL in test
crt/testcases/t_global_ctors: New test
Revert "crt: Cleanup gcc c++ ctors and dtors, do not use atexit() for DLL builds"
headers: Add missing `extern "C"` in corecrt.h