i386: Add tests for lfence with load/indirect branch/ret

Add tests for -mlfence-after-load=, -mlfence-before-indirect-branch=
and -mlfence-before-ret=.

	* testsuite/gas/i386/i386.exp: Run new tests.
	* testsuite/gas/i386/lfence-byte.d: New file.
	* testsuite/gas/i386/lfence-byte.e: Likewise.
	* testsuite/gas/i386/lfence-byte.s: Likewise.
	* testsuite/gas/i386/lfence-indbr-a.d: Likewise.
	* testsuite/gas/i386/lfence-indbr-b.d: Likewise.
	* testsuite/gas/i386/lfence-indbr-c.d: Likewise.
	* testsuite/gas/i386/lfence-indbr.e: Likewise.
	* testsuite/gas/i386/lfence-indbr.s: Likewise.
	* testsuite/gas/i386/lfence-load.d: Likewise.
	* testsuite/gas/i386/lfence-load.s: Likewise.
	* testsuite/gas/i386/lfence-ret-a.d: Likewise.
	* testsuite/gas/i386/lfence-ret-b.d: Likewise.
	* testsuite/gas/i386/lfence-ret.s: Likewise.
	* testsuite/gas/i386/x86-64-lfence-byte.d: Likewise.
	* testsuite/gas/i386/x86-64-lfence-byte.e: Likewise.
	* testsuite/gas/i386/x86-64-lfence-byte.s: Likewise.
	* testsuite/gas/i386/x86-64-lfence-indbr-a.d: Likewise.
	* testsuite/gas/i386/x86-64-lfence-indbr-b.d: Likewise.
	* testsuite/gas/i386/x86-64-lfence-indbr-c.d: Likewise.
	* testsuite/gas/i386/x86-64-lfence-indbr.e: Likewise.
	* testsuite/gas/i386/x86-64-lfence-indbr.s: Likewise.
	* testsuite/gas/i386/x86-64-lfence-load.d: Likewise.
	* testsuite/gas/i386/x86-64-lfence-load.s: Likewise.
	* testsuite/gas/i386/x86-64-lfence-ret-a.d: Likewise.
	* testsuite/gas/i386/x86-64-lfence-ret-b.d: Likewise.