Set a new variable to signify if the final target is an embedded
system.
* scripttempl/{mips.sc,elfmips.sc}: Don't add SIZEOF_HEADERS to
.text for an embedded system.
* Makefile.in (GENSCRIPTS): Pass @host@ @target@ @target_alias@.
* genscripts.sh: Set host, target and target_alias variables.
Check for native compile by comparing ${target} and ${host}.
* emultempl/elf32.em: Likewise.
* scripttempl/elfmips.sc: Test ${target}, not ${target_alias}.