i386: Update I386_USE_SYSENTER for early PIC syscall

Define I386_USE_SYSENTER to 0 or 1 so that special versions of syscalls
with "int $0x80" can be provided for static PIE during self relocation.
Also check PIC instead SHARED for PIC version of syscall macros.

	* sysdeps/unix/sysv/linux/i386/sysdep.h (I386_USE_SYSENTER):
	Define to I386_USE_SYSENTER to 0 or 1 if not defined.
	(ENTER_KERNEL): Check if I386_USE_SYSENTER is 1 and check PIC.
	(INTERNAL_SYSCALL_MAIN_INLINE): Likewise.
	(INTERNAL_SYSCALL_NCS): Likewise.
	(LOADARGS_1): Likewise.
	(LOADARGS_5): Likewise.
	(RESTOREARGS_1): Likewise.
	(RESTOREARGS_5): Likewise.