dwarf2read: move producers help functions to a dwarf specific file
    
    This patch add new files to add dwarf reader utilities into it.
    It is also a preparation path to add functions to detect the icc
    version that produced a given compilation unit.
    
    2017-09-18  Walfred Tedeschi  <walfred.tedeschi@intel.com>
    
    	* Makefile.in (SFILES): Add dwarf2utils.c.
    	(COMMON_OBS): Add dwarf2utils.o
    	* amd64-tdep.c (dwarf2utils.h): Add new header.
    	* dwarf2read.c (dwarf2utils.h): Add new header.
    	* dwarf2utils.c: New file.
    	* dwarf2utils.h: New file.
    	* utils.c (producer_is_gcc, producer_is_gcc_ge_4): Move to
    	dwarf2utils.c.
    	* utils.h (producer_is_gcc, producer_is_gcc_ge_4): Move to
    	dwarf2utils.h.