remove STRUCT_VALUE macro

remove STRUCT_VALUE macro

This macro was converted to the TARGET_STRUCT_VALUE_RTX hook many years
ago, however there are still some lingering definitions, and a use in
libobjc.  All the remaining definitions define the macro to 0, which
libobjc treats the same as undefined, so it won't break anything else to
have libobjc stop checking the macro.  However it may be that this part
of libobjc has been broken for a long time on targets that only define
the hook, but that is a separate issue.

gcc/ChangeLog:

2015-09-12  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* config/arc/arc.h: Remove define of STRUCT_VALUE.
	* config/lm32/lm32.h: Likewise.
	* config/mep/mep.h: Likewise.
	* config/visium/visium.h: Likewise.
	* system.h: Poison STRUCT_VALUE macro.

libobjc/ChangeLog:

2015-09-12  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	PR libobjc/24775
	* sendmsg.c: Remove check of STRUCT_VALUE macro.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@227710 138bc75d-0d04-0410-961f-82ee72b054a4