octeon-exts-2.c: Compile it with -meb.

	* gcc.target/mips/octeon-exts-2.c: Compile it with -meb.
	* gcc.target/mips/octeon-exts-5.c: New test.
	* gcc.target/mips/octeon-bbit-3.c: Compile with -meb.  Add
	comment why this is necessary.

From-SVN: r140988