Add getentropy(2)'s syscall number as a const
Add getentropy(2)'s syscall number as a const

I'm not convinced that the NR_* naming scheme is ideal, but it's pretty
good.

I didn't recognize any other syscall numbers in the file, so I started a
new section.

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