Add -mno-shared to x86 assembler

Add -mno-shared to x86 assembler

On ELF target, the assembler normally generates code which can go into a
shared library where non-weak symbols can be preempted.  The -mno-shared
option tells the assembler to generate code not for a shared library,
where non-weak symbols won't be preempted.  The resulting code is slightly
smaller.  This option mainly affects the handling of branch instructions.

gas/

	* config/tc-i386.c (no_shared): New.
	(OPTION_MNO_SHARED): Likewise.
	(elf_symbol_resolved_in_segment_p): Check no_shared.
	(md_longopts): Add mno-shared.
	(md_parse_option): Handle OPTION_MNO_SHARED.
	(md_show_usage): Add -mno-shared.
	* doc/c-i386.texi: Document -mno-shared.

gas/testsuite/

	* gas/i386/i386.exp: Run relax-4 and x86-64-relax-3.
	* gas/i386/relax-4.d: New file.
	* gas/i386/x86-64-relax-3.d: Likewise.