Add abort
Add abort

This is defined by the C standard to indicate abnormal program
terminaiton; it is defined to call raise(SIGABRT), and to not return.
This can be useful when panics are not an option, such as signal
handlers handling stack overflow.

cactorium/libc,rust-lang/libc,superriva/libc,cybergeek94/libc,cactorium/libc,anatol/libc,cactorium/libc,zethra/libc,mneumann/libc,rust-lang/libc,superriva/libc,philippkeller/libc,rust-lang/libc,cybergeek94/libc,cybergeek94/libc,rust-lang-nursery/libc,rust-lang-nursery/libc,superriva/libc,mneumann/libc,philippkeller/libc,rust-lang-nursery/libc,anatol/libc,zethra/libc,zethra/libc,philippkeller/libc,mneumann/libc,anatol/libc