Fix clang build for using DR in google3

None of these are bugs in core DR.

- parse_int(): base is unsigned, comparing vs 0 is tautological
- atomic_compare_exchange_int64(): the inline asm is invalid on ia32, but
  gcc doesn't complain since it is unused
- init_patch_list(): clang says the comparison vs USHORT_MAX is
  tautological based on the range of the enum type.  Casting to int
  silences the warning.
- linux.fib-static: Clang can't link libc with -static and -rdynamic,
  which is in the default CMAKE_SHARED_LIBRARY_LINK_C_FLAGS.  Adding
  -Wl,--no-export-dynamic makes it work.
- linux.vfork run_child(): no return from non-void function

Review URL: https://codereview.appspot.com/7093063

git-svn-id: https://dynamorio.googlecode.com/svn/trunk@1826 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6
Merge branch 'master' into fix-clang