rustdoc: Filter out private definitions. Closes #3538
auto merge of #5375 : z0w0/rust/rustdoc-private-hide, r=thestinger
llvm splitstack update
rust morestack assembly for arm

Conflicts:
	src/rt/arch/arm/morestack.S
llvm change update
Normalize target triple so that llvm can recognize target os correctly
Fix an android compilation fail