MIPS: Added support for Loongson architectures.

src/mips/constants-mips.h

Index: src/mips/constants-mips.h
diff --git a/src/mips/constants-mips.h b/src/mips/constants-mips.h
index d62a8901f0ad0a0ffe497a9b8e655759fc4a9b7a..d909296056adbe56e3b3cb6814ec407ac7a2b191 100644
--- a/src/mips/constants-mips.h
+++ b/src/mips/constants-mips.h
@@ -39,11 +39,20 @@
 
 #define UNSUPPORTED_MIPS() v8::internal::PrintF("Unsupported instruction.\n")
 
+enum ArchVariants {
+  kMips32r2,
+  kMips32r1,
+  kLoongson
+};
 
 #ifdef _MIPS_ARCH_MIPS32R2
-  #define mips32r2 1
+  static const ArchVariants kArchVariant = kMips32r2;
+#elif _MIPS_ARCH_LOONGSON
+// The loongson flag refers to the LOONGSON architectures based on MIPS-III,
+// which predates (and is a subset of) the mips32r2 and r1 architectures.
+  static const ArchVariants kArchVariant = kLoongson;
 #else
-  #define mips32r2 0
+  static const ArchVariants kArchVariant = kMips32r1;
 #endif