Fix wxStaticText::Disable() to respect text color on OS X

wxStaticText emulates disabled state on OS X by changing text color to
light grey. When re-enabling the control, though, it always set the
color to the standard text color, which broke static texts with a custom
color.

Fix this by keeping track of the original color and restoring it back
when setEnabled:YES is called.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78107 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Correction for non-precomp compilation

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78109 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775