Link with -lrt if glibc < 2.17 for native on linux
fix ucontext.h include for OSX, FreeBSD
fix signal handler, ringbuffer for native FreeBSD
* function to check for enabled interrupts on ARM
* added TODO comment
Merge branch 'master' of github.com:RIOT-OS/RIOT
clarify: while loop without body is correct here
prevent double include of debug.h
main should always return int

this fixes some compiler warnings