Zebediah Figura (@zfigura) commented about dlls/comdlg32/cdlg32.c:
DECLSPEC_HIDDEN HINSTANCE COMDLG32_hInstance = 0; +DECLSPEC_HIDDEN HANDLE COMDLG32_hActCtx = INVALID_HANDLE_VALUE;
Despite the impression given by the previous line, you don't need to specify DECLSPEC_HIDDEN in the .c file if it's already specified in the header.