MIPS64: Improve long branches utilizing code range.

src/mips64/constants-mips64.h

Index: src/mips64/constants-mips64.h
diff --git a/src/mips64/constants-mips64.h b/src/mips64/constants-mips64.h
index 37de91a0e2318d99f52f2b27b5e1d8ba86181754..ec141283728d37d96f55138569c46f449b5ead6e 100644
--- a/src/mips64/constants-mips64.h
+++ b/src/mips64/constants-mips64.h
@@ -959,7 +959,7 @@ class Instruction {
     return Bits(kImm21Shift + kImm21Bits - 1, kImm21Shift);
   }
 
-  inline int32_t Imm26Value() const {
+  inline int64_t Imm26Value() const {
     DCHECK(InstructionType() == kJumpType);
     return Bits(kImm26Shift + kImm26Bits - 1, kImm26Shift);
   }