x86: Add sysdeps/x86/sysdep.h

Add a new header file, sysdeps/x86/sysdep.h, for common assembly code
macros between i386 and x86-64.  Tested on i686 and x86-64.  There are
no differences in outputs of "readelf -a" and "objdump -dw" on all glibc
shared objects before and after the patch.

	* sysdeps/i386/sysdep.h: Include <sysdeps/x86/sysdep.h> instead
	of <sysdeps/generic/sysdep.h>.
	(ALIGNARG): Removed.
	(ASM_SIZE_DIRECTIVE): Likewise.
	(ENTRY): Likewise.
	(END): Likewise.
	(ENTRY_CHK): Likewise.
	(END_CHK): Likewise.
	(syscall_error): Likewise.
	(mcount): Likewise.
	(PSEUDO_END): Likewise.
	(L): Likewise.
	(atom_text_section): Likewise.
	* sysdeps/x86/sysdep.h: New file.
	* sysdeps/x86_64/sysdep.h: Include <sysdeps/x86/sysdep.h> instead
	of <sysdeps/generic/sysdep.h>.
	(ALIGNARG): Removed.
	(ASM_SIZE_DIRECTIVE): Likewise.
	(ENTRY): Likewise.
	(END): Likewise.
	(ENTRY_CHK): Likewise.
	(END_CHK): Likewise.
	(syscall_error): Likewise.
	(mcount): Likewise.
	(PSEUDO_END): Likewise.
	(L): Likewise.
	(atom_text_section): Likewise.