scons: Fixes uninitialized warnings issued by clang

Small fixes to appease recent clang versions.

src/arch/arm/insts/fplib.cc

@@ -2509,7 +2509,7 @@ fplibRecipEstimate(uint32_t op, FPSCR &fpscr)
         result = fp32_infinity(sgn);
         flags |= FPLIB_DZC;
     } else if (!((uint32_t)(op << 1) >> 22)) {
-        bool overflow_to_inf;
+        bool overflow_to_inf = false;
         switch (FPCRRounding(fpscr)) {
           case FPRounding_TIEEVEN:
             overflow_to_inf = true;
@@ -2570,7 +2570,7 @@ fplibRecipEstimate(uint64_t op, FPSCR &fpscr)
         result = fp64_infinity(sgn);
         flags |= FPLIB_DZC;
     } else if (!((uint64_t)(op << 1) >> 51)) {
-        bool overflow_to_inf;
+        bool overflow_to_inf = false;
         switch (FPCRRounding(fpscr)) {
           case FPRounding_TIEEVEN:
             overflow_to_inf = true;

src/base/compiler.hh

@@ -50,6 +50,13 @@
 #define M5_PRAGMA_NORETURN(x)
 #define M5_DUMMY_RETURN
 #define M5_VAR_USED __attribute__((unused))
+
+#if defined(__clang__)
+#define M5_CLASS_VAR_USED M5_VAR_USED
+#else
+#define M5_CLASS_VAR_USED
+#endif
+
 #define M5_ATTR_PACKED __attribute__ ((__packed__))
 #define M5_NO_INLINE __attribute__ ((__noinline__))
 #else

src/cpu/o3/scoreboard.hh

@@ -72,7 +72,7 @@ class Scoreboard
      * the misc registers that come after the physical registers and
      * which are hardwired to be always considered ready.
      */
-    unsigned numTotalRegs;
+    unsigned M5_CLASS_VAR_USED numTotalRegs;
 
     /** The index of the zero register. */
     PhysRegIndex zeroRegIdx;

src/sim/probe/probe.hh

@@ -133,7 +133,7 @@ class ProbeManager
 {
   private:
     /** Required for sensible debug messages.*/
-    const SimObject *object;
+    const M5_CLASS_VAR_USED SimObject *object;
     /** Vector for name look-up. */
     std::vector<ProbePoint *> points;