Platform/Platform-specific build defines

In the Gecko code we have a bunch of preprocessor conditions that help us conditionally compile code for specific platforms. These can get confusing so here is a handy-dandy table to help you keep them straight.

OS	Windows		OS X		Linux-gtk			Android		iOS
Product	Desktop	B2G	Desktop	B2G	Desktop	B2G	Mulet	Fennec	B2G	iOS
XP_WIN	true	true	false	false	false	false	false	false	false	false
XP_DARWIN	false	false	true	true	false	false	false	false	false	true
XP_MACOSX	false	false	true	true	false	false	false	false	false	false
XP_IOS	false	false	false	false	false	false	false	false	false	true
XP_LINUX	false	false	false	false	true	true	true	true	true	false
ANDROID	false	false	false	false	false	false	false	true	true	false
MOZ_B2G	false	true	false	true	false	true	true	false	true	false
MOZ_WIDGET_GTK	false	false	false	false	true	true	true	false	false	false
MOZ_WIDGET_ANDROID	false	false	false	false	false	false	false	true	false	false
MOZ_WIDGET_GONK	false	false	false	false	false	false	false	false	true	false
MOZ_WIDGET_UIKIT	false	false	false	false	false	false	false	false	false	true