Add and use sysdeps/i386/link-defines.sym

Define macros for fields in La_i86_regs and La_i86_retval and use them
in dl-trampoline.S, instead of hardcoded values.

	* sysdeps/i386/Makefile (gen-as-const-headers)[elf]: Add
	link-defines.sym.
	* sysdeps/i386/dl-trampoline.S: Include <link-defines.h>.
	(_dl_runtime_profile): Use LONG_DOUBLE_SIZE, LRV_SIZE,
	LRV_EAX_OFFSET, LRV_EDX_OFFSET, LRV_ST0_OFFSET, LRV_ST1_OFFSET
	and LR_SIZE.
	* sysdeps/i386/link-defines.sym: New file.