mark the assembly object stacks as non-executable

Closes #5643

This also removes the need to pass noexecstack to gcc, but that wasn't
actually working anymore.
install.mk: use INSTALL_LIB for all libraries

There's no reason to make them executable, and this throws a warning
with the Arch Linux package lint tool (namcap) for .a files.
auto merge of #5647 : thestinger/rust/execstack, r=brson

Closes #5643
auto merge of #5649 : thestinger/rust/lib, r=brson

There's no reason to make them executable, and this throws a warning
with the Arch Linux package lint tool (namcap) for .a files.
Update tutorial.md

Change fn() -> &fn().
auto merge of #5651 : luqmana/rust/incoming, r=thestinger

Change fn() -> &fn().
auto merge of #5653 : brson/rust/warnings, r=brson
rt/arch/arm: fix syntax used for noexec stack
auto merge of #5655 : thestinger/rust/arm, r=brson

Turns out @ isn't valid for the ARM assembler.
core: Update libc docs to clarify usage
doc: Update tutorial description of core