Add signalfd call to bionic

Add signalfd() call to bionic.

Adding the signalfd call was done in 3 steps:
- add signalfd4 system call (function name and syscall
  number) to libc/SYSCALLS.TXT
- generate all necessary headers by calling
  libc/tools/ This patch is adding
  the generated files since the build system
  does not call
- create the signalfd wrapper in signalfd.cpp and add
  the function prototype to sys/signalfd.h

Change-Id: I7ee1d3e60d5d3e1c73d9820e07d23b9ce6e1a5ab
12 files changed