Fixes a problem compiling on sparcs where STRUCT_VALUE is defined in
sparc.h to use gen_rtx_MEM() and then evaluated in an #if directive in
sendmsg.c.
        * objc/sendmsg.c: Define gen_rtx_MEM() to 1, as is already done
        for gen_rtx(MEM, ...).

From-SVN: r19353