windows: libgcc_s DLL is needed
windows: add executable bit to GCC origin DLL

DLL needs executable bit.
fix compilation error not found `cairo-quartz-image.h`

`cairo-quratz-image.h` is not always installed.
Simply installation cairo in OS X with Homebrew as follows:

    % brew install cairo

Homebrew's cairo Bottle is not fully enabled quartz feature.
So, it is not installed `cairo-quartz-image.h`.
This lack of existence of `cairo-quartz-image.h` causes following error:

```log
compiling rb_cairo_surface.c
rb_cairo_surface.c:58:14: fatal error: 'cairo-quartz-image.h' file not
found
 #    include <cairo-quartz-image.h>
              ^
			  1 error generated.
			  make[1]: *** [rb_cairo_surface.o] Error 1
			  make: *** [all] Error 2
```

Instead, following installation is also installing `cairo-quartz-image.h`

    % brew install cairo --without-x11

It seems that it needs check `cairo-quartz-image.h` existence before it include `cairo-quartz-image.h`.
use CAIRO_HAS_QUARTZ_IMAGE_SURFACE in rb_cairo_surface.c
remove needless checking header existence
Merge pull request #31 from cosmo0920/fix-compile-error-quartz-image

fix compilation error not found `cairo-quartz-image.h` in OS X

Patch by Hiroshi Hatake. Thanks!!!