Implement byte swapping instructions on MIPS32 and MIPS64.

src/mips64/assembler-mips64.h

Index: src/mips64/assembler-mips64.h
diff --git a/src/mips64/assembler-mips64.h b/src/mips64/assembler-mips64.h
index f93bc48837ff91c8a93fa3c2eb68ad678eda833b..783db0006c21100c85ddfa6dac9966d653c686eb 100644
--- a/src/mips64/assembler-mips64.h
+++ b/src/mips64/assembler-mips64.h
@@ -907,6 +907,12 @@ class Assembler : public AssemblerBase {
   void align(Register rd, Register rs, Register rt, uint8_t bp);
   void dalign(Register rd, Register rs, Register rt, uint8_t bp);
 
+  void wsbh(Register rd, Register rt);
+  void dsbh(Register rd, Register rt);
+  void dshd(Register rd, Register rt);
+  void seh(Register rd, Register rt);
+  void seb(Register rd, Register rt);
+
   // --------Coprocessor-instructions----------------
 
   // Load, store, and move.