data-to-c.py: autodetect line endings

When GLib code is checked out with Windows line endings (happens on Windows),
data-to-c.py embedded that line endings into generated string literal. And
then they translated to double newlines in glib-compile-resources output.

clang-cl failed to compile such files because of empty lines in the middle of
multiline macros:

    #define G_MSVC_CTOR(_func,_sym_prefix) \

      static void _func(void); \

To fix the issue, enable 'universal newlines' mode when reading the input in
data-to-c.py - translate both '\n' and '\r\n' to '\n'.

Fixes GNOME/glib#2340
10 jobs for fix-data-to-c-line-endings in 23 minutes and 29 seconds (queued for 1 second)