Customized header search paths

1. Use "-I <path>" (or "--include-path <path>") to add a header search path.
2. You can specify more than 1 search path and the preceding path takes precedence.
3. System include path is moved out of the code -- they are inserted in the build system instead.

Change-Id: Idfaee4763e8bf0cd71deeecdf1dc1ec515e44d0f
5 files changed