Introduce two DWARF attribute extentions DW_AT_APPLE_optimized, DW_AT_APPLE_flags.

DW_AT_APPLE_optimized flag is set when a compile_unit is optimized. The debugger takes advantage of this information some way.

DW_AT_APPLE_flags encodes command line options when certain env. variable is set. This is used by build engineers to track various gcc command lines used by by  a project, irrespective of whether the project used makefile, Xcode or something else.

llvm-gcc patch is next.

llvm-svn: 62888