fix compiler flags in ytk and ydk on OSX (define DISABLE_VISIBILITY)

[paseri3739]

Added DISABLE_VISIBILITY to compile patched GTK+ on OSX correctly.

[x42]

Why is this patch needed? and why would you want to disable visibility? gdk/gtk internal functions should remain hidden, no?

[tkysfjk]

@paseri3739 @x42
Seems that this relates to error: aliases are not supported on darwin.
I found alternative solution which uses CFLAGS/CPPFLAGS with --keepflags waf option instead of modifying codes.

ex.

$ PKG_CONFIG_PATH="$PKG_CONFIG_PATH:/opt/homebrew/opt/libarchive/lib/pkgconfig" \
    CPPFLAGS="-DDISABLE_VISIBILITY -I/opt/homebrew/include -I/opt/homebrew/Cellar/libarchive/3.7.7/include" \
    CFLAGS="-DDISABLE_VISIBILITY -I/opt/homebrew/include -I/opt/homebrew/Cellar/libarchive/3.7.7/include" \
    LDFLAGS="-L/opt/homebrew/lib -L/opt/homebrew/Cellar/libarchive/3.7.7/lib" \
    ./waf configure --keepflags

[pauldavisthefirst]

I would still like some explanation on why you feel this change is required.