util::shared: Fix nightly churn
util::shared: Allow dead code for NoInterrupts
util::shared: Always compile

This really isn't specific to multitasking
os::cond_var: Dust off and add single-threaded implementation
os::cond_var: Always compile
cortex: Move NoInterrupts to common
mutex: Style fixes
mutex: Single threaded implementation
mutex: Always compile
Merge pull request #194 from bgamari/concurrency

Concurrency  primitives
lang_items: Silence unused argument warning
k20::sim: Fix non-snake-case warning
drivers::chario: Kill unused use
isrs: Silence non-upper-case-globals warning
Merge pull request #196 from bgamari/misc

Miscellaneous warnings fixes
cond_var: Use wfi() instead of asm!("wfi")

Forgot the "volatile" in the open coded version
cond_var: Fix inverted logic; a race condition remains
Use -C no-stack-check instead of #[no_stack_check]
util::support: Add __aeabi_memset

This is helpful to have when compiling without optimization
Merge pull request #198 from bgamari/misc

Miscellaneous fixes