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.

main_test.go

@@ -37,6 +37,7 @@ var supportedLinuxArches = map[string]string{
 	"X86Linux":   "linux/386",
 	"ARMLinux":   "linux/arm/6",
 	"ARM64Linux": "linux/arm64",
+	"MIPSLinux":  "linux/mipsle",
 	"WASIp1":     "wasip1/wasm",
 }
 
@@ -211,6 +212,12 @@ func runPlatTests(options compileopts.Options, tests []string, t *testing.T) {
 				continue
 			}
 		}
+		if options.GOOS == "linux" && (options.GOARCH == "mips" || options.GOARCH == "mipsle") {
+			if name == "atomic.go" {
+				// 64-bit atomic operations aren't currently supported on MIPS.
+				continue
+			}
+		}
 		if options.Target == "simavr" {
 			// Not all tests are currently supported on AVR.
 			// Skip the ones that aren't.