Jit64: Invalidate cached constant values w/o host register on flush

If we don't flush the values, they persist in the register cache,
potentially resulting in the values being out of sync with PPCSTATE.

This was causing random crashes in games, mainly booting, when certain
JIT instructions were disabled, or forced to fall back to interpreter.

Source/Core/Core/PowerPC/Jit64/JitRegCache.cpp

@@ -101,6 +101,13 @@ void RegCache::Flush(FlushMode mode, BitSet32 regsToFlush)
         ASSERT_MSG(DYNA_REC, 0, "Jit64 - Flush unhandled case, reg %u PC: %08x", i, PC);
       }
     }
+    else if (m_regs[i].location.IsImm())
+    {
+      // We can have a cached value without a host register through speculative constants.
+      // It must be cleared when flushing, otherwise it may be out of sync with PPCSTATE,
+      // if PPCSTATE is modified externally (e.g. fallback to interpreter).
+      m_regs[i].location = GetDefaultLocation(i);
+    }
   }
 }