Define uint64_t constants with ULL suffix

Fixes https://github.com/harfbuzz/harfbuzz/issues/901

src/hb-private.hh

diff --git a/src/hb-private.hh b/src/hb-private.hh
index 62a103c..e34e5c7 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -414,7 +414,7 @@
   if (sizeof (T) <= 8)
   {
     /* "bithacks" */
-    const uint64_t b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000, 0xFFFFFFFF00000000};
+    const uint64_t b[] = {0x2ULL, 0xCULL, 0xF0ULL, 0xFF00ULL, 0xFFFF0000ULL, 0xFFFFFFFF00000000ULL};
     const unsigned int S[] = {1, 2, 4, 8, 16, 32};
     unsigned int r = 0;
     for (int i = 5; i >= 0; i--)