Revert "Revert "Upgrade to 5.0.71.48"" DO NOT MERGE

This reverts commit f2e3994fa5148cc3d9946666f0b0596290192b0e,
and updates the x64 makefile properly so it doesn't break that
build.

FPIIM-449

Change-Id: Ib83e35bfbae6af627451c926a9650ec57c045605
(cherry picked from commit 109988c7ccb6f3fd1a58574fa3dfb88beaef6632)
diff --git a/src/mips/disasm-mips.cc b/src/mips/disasm-mips.cc
index 936514a..7e0a480 100644
--- a/src/mips/disasm-mips.cc
+++ b/src/mips/disasm-mips.cc
@@ -1500,6 +1500,7 @@
         if (rs_reg >= rt_reg) {
           Format(instr, "bovc  'rs, 'rt, 'imm16s -> 'imm16p4s2");
         } else {
+          DCHECK(rt_reg > 0);
           if (rs_reg == 0) {
             Format(instr, "beqzalc 'rt, 'imm16s -> 'imm16p4s2");
           } else {
@@ -1516,6 +1517,7 @@
         if (rs_reg >= rt_reg) {
           Format(instr, "bnvc  'rs, 'rt, 'imm16s -> 'imm16p4s2");
         } else {
+          DCHECK(rt_reg > 0);
           if (rs_reg == 0) {
             Format(instr, "bnezalc 'rt, 'imm16s -> 'imm16p4s2");
           } else {