add linux mips assembler for gas ABI o32

Since the two assembly examples for MIPS are targeting the SPIM, A MIPS32 Simulator, I felt appropriate to add a Linux version for the same targeting the common o32 ABI.
Can be tested on x86 Linux using qemu and cross gcc.

The following is for mipsel:

$ mipsel-linux-gnu-as -mips32 -EL a/Assembler_mipsel_linux.s -o /tmp/hello.o
$ mipsel-linux-gnu-ld /tmp/hello.o -o hello
$ qemu-mipsel ./hello

a/Assembler_mipsel_linux.s

@@ -0,0 +1,15 @@
+		.rdata
+		.align		2
+hello:		.asciz		"Hello world\n"<0>
+		.align		4
+length:		.word		. - hello
+		.text
+		.globl		__start
+__start:
+		move		$a0,$0
+		la		$a1,hello
+		lw		$a2,length
+		li		$v0,0xfa4
+		syscall
+		li		$v0,0xfa1
+		syscall