Add some additional headers to gen_constants.sh

This change allows the use of the various RLIMIT_*, termios (to get some
ioctl() commands), as well as adding an underscore to the regex so that
S_IFIFO (which expands to __S_IFIFO) could be added.

Bug: None
Test: Can parse a policy with RLIMIT_CPU, ARCH_SET_FS
Change-Id: Ie6c4a0cf004d8aebfdcf7e070c9480bc53220fc0
1 file changed