[sanitizer] Fix shift UB in LEB128 test

If u64 and uptr have the same size, then this will perform a shift
by the bitwidth, which is UB. We only need this code if uptr is
smaller than u64.

compiler-rt/lib/sanitizer_common/tests/sanitizer_leb128_test.cpp

@@ -25,10 +25,12 @@ static uptr BitsNeeded(u64 v) {
   if (!v)
     return 1;
   uptr r = 0;
-  uptr uptr_bits = 8 * sizeof(uptr);
-  while (v >> uptr_bits) {
-    r += uptr_bits;
-    v >>= uptr_bits;
+  if (sizeof(uptr) != sizeof(u64)) {
+    uptr uptr_bits = 8 * sizeof(uptr);
+    while (v >> uptr_bits) {
+      r += uptr_bits;
+      v >>= uptr_bits;
+    }
   }
   return r + MostSignificantSetBitIndex(v) + 1;
 }