build: remove GCC_WARN_ABOUT_MISSING_NEWLINE

Not compatible with non-Apple gcc builds.  Fixes the following build
error:

    gcc-4.8: error: unrecognized command line option '-Wnewline-eof'
darwin: fix 10.6 build error in fsevents.c

Work around an 'initializer element is not constant' build error in
src/unix/fsevents.c by turning the const int flags into #defines.

Only an issue on OS X 10.6 due to the old compiler it uses.

Fixes #908.

This is a back-port of commit 82f2472 from the master branch.