S390: Fixed s390 simulation check for underflow in subtraction.

Clang optimizes away CheckOverflowForIntSub at any opt
level (includes -O1, -O2, -O3) into a false statement,
resulting in incorrect values being returned. As the C++
standard considers overflows to be undefined behaviour,
this is technically correct as compilers can assume that
overflows never occur, but problematic in our case (where
overflows do occur, and a specific result is expected).

This change replaces the original check with a call to a
function that is optimized in a manner that returns correct output.

R=michael_dawson@ca.ibm.com,jyan@ca.ibm.com,mtbrandyberry@ca.ibm.com,joransiu@ca.ibm.com,danno@chromium.org,jkummerow@chromium.org,jochen@chromium.org

BUG=

Review URL: https://codereview.chromium.org/1826043002

Cr-Commit-Position: refs/heads/master@{#35082}

src/s390/simulator-s390.h

@@ -258,8 +258,8 @@ class Simulator {
   // Helper functions to set the conditional flags in the architecture state.
   bool CarryFrom(int32_t left, int32_t right, int32_t carry = 0);
   bool BorrowFrom(int32_t left, int32_t right);
-  bool OverflowFrom(int32_t alu_out, int32_t left, int32_t right,
-                    bool addition);
+  template <typename T1>
+  inline bool OverflowFromSigned(T1 alu_out, T1 left, T1 right, bool addition);
 
   // Helper functions to decode common "addressing" modes
   int32_t GetShiftRm(Instruction* instr, bool* carry_out);