all: add linux/mipsle support

This adds linux/mipsle (little endian Mips) support to TinyGo.

It also adds experimental linux/mips (big-endian) support. It doesn't
quite work yet, some parts of the standard library (like the reflect
package) currently seem to assume a little-endian system.

compiler/defer.go

@@ -187,6 +187,18 @@ std z+5, r29
 ldi r24, 0
 1:`
 		constraints = "={r24},z,~{r0},~{r2},~{r3},~{r4},~{r5},~{r6},~{r7},~{r8},~{r9},~{r10},~{r11},~{r12},~{r13},~{r14},~{r15},~{r16},~{r17},~{r18},~{r19},~{r20},~{r21},~{r22},~{r23},~{r25},~{r26},~{r27}"
+	case "mips":
+		// $4 flag (zero or non-zero)
+		// $5 defer frame
+		asmString = `
+.set noat
+move $$4, $$zero
+jal 1f
+1:
+addiu $$ra, 8
+sw $$ra, 4($$5)
+.set at`
+		constraints = "={$4},{$5},~{$1},~{$2},~{$3},~{$5},~{$6},~{$7},~{$8},~{$9},~{$10},~{$11},~{$12},~{$13},~{$14},~{$15},~{$16},~{$17},~{$18},~{$19},~{$20},~{$21},~{$22},~{$23},~{$24},~{$25},~{$26},~{$27},~{$28},~{$29},~{$30},~{$31},~{$f0},~{$f1},~{$f2},~{$f3},~{$f4},~{$f5},~{$f6},~{$f7},~{$f8},~{$f9},~{$f10},~{$f11},~{$f12},~{$f13},~{$f14},~{$f15},~{$f16},~{$f17},~{$f18},~{$f19},~{$f20},~{$f21},~{$f22},~{$f23},~{$f24},~{$f25},~{$f26},~{$f27},~{$f28},~{$f29},~{$f30},~{$f31},~{memory}"
 	case "riscv32":
 		asmString = `
 la a2, 1f