Fix errors reported by cppcheck in src/libm/sleefsp.c

Error: integer overflow
Fix: Use appropriate intermediate type. UL should be big enough
     on all platforms.

src/libm/sleefsp.c

@@ -53,11 +53,11 @@ static INLINE CONST float fabsfk(float x) {
 }
 
 static INLINE CONST float mulsignf(float x, float y) {
-  return intBitsToFloat(floatToRawIntBits(x) ^ (floatToRawIntBits(y) & (1 << 31)));
+  return intBitsToFloat(floatToRawIntBits(x) ^ (floatToRawIntBits(y) & 0x80000000U));
 }
 
 static INLINE CONST float copysignfk(float x, float y) {
-  return intBitsToFloat((floatToRawIntBits(x) & ~(1 << 31)) ^ (floatToRawIntBits(y) & (1 << 31)));
+  return intBitsToFloat((floatToRawIntBits(x) & ~0x80000000U) ^ (floatToRawIntBits(y) & 0x80000000U));
 }
 
 static INLINE CONST float signf(float d) { return mulsignf(1, d); }
@@ -1920,11 +1920,11 @@ EXPORT CONST float xnextafterf(float x, float y) {
   cxf = x == 0 ? mulsignf(0, y) : x;
   memcpy(&cxi, &cxf, sizeof(cxi));
   int c = (cxi < 0) == (y < x);
-  if (c) cxi = -(cxi ^ (1 << 31));
+  if (c) cxi = -(cxi ^ 0x80000000U);
 
   if (x != y) cxi--;
 
-  if (c) cxi = -(cxi ^ (1 << 31));
+  if (c) cxi = -(cxi ^ 0x80000000U);
 
   memcpy(&cxf, &cxi, sizeof(cxf));
   if (cxf == 0 && x != 0) cxf = mulsignf(0, x);