ELF: Updated comments for ET_EXEC and ET_DYN

ELF: Updated comments for ET_EXEC and ET_DYN

include/elf/common.h has

 #define ET_EXEC         2       /* Executable file */
 #define ET_DYN          3       /* Shared object file */

These predate PIE:

https://groups.google.com/forum/#!topic/generic-abi/mBKlSNldFW4

Updated comments to

 #define ET_EXEC         2       /* Position-dependent executable file */
 #define ET_DYN          3       /* Position-independent executable or
                                    shared object file */

	* elf/common.h: Update comments for ET_EXEC and ET_DYN.