[libc][NFC] fix sprintf test on 32 bit systems

[michaelrj]

Summary

The expected number for the max ptrdiff value was expected to be exactly
4294967296 (232) for 32 bit systems, when it should be
4294967295 (232 - 1). This also adds a second test to check for this
case on non-32 bit systems.

libc/test/src/stdio/sprintf_test.cpp

TEST(LlvmLibcSPrintfTest, IntConv) {
   written = __llvm_libc::sprintf(buff, "%hhu", 257); // 0x101
   EXPECT_EQ(written, 1);
   ASSERT_STREQ(buff, "1");
 
   written = __llvm_libc::sprintf(buff, "%llu", 18446744073709551615ull);
   EXPECT_EQ(written, 20);
   ASSERT_STREQ(buff, "18446744073709551615"); // ull max
 
+  written = __llvm_libc::sprintf(buff, "%u", ~0);
+  if (sizeof(int) == 4) {
+    EXPECT_EQ(written, 10);
+    ASSERT_STREQ(buff, "4294967295");
+  }
+
   written = __llvm_libc::sprintf(buff, "%tu", ~ptrdiff_t(0));
   if (sizeof(ptrdiff_t) == 8) {
     EXPECT_EQ(written, 20);
     ASSERT_STREQ(buff, "18446744073709551615");
   } else if (sizeof(ptrdiff_t) == 4) {
     EXPECT_EQ(written, 10);
-    ASSERT_STREQ(buff, "4294967296");
+    ASSERT_STREQ(buff, "4294967295");
   }
 
   written = __llvm_libc::sprintf(buff, "%lld", -9223372036854775807ll - 1ll);
   EXPECT_EQ(written, 20);
   ASSERT_STREQ(buff, "-9223372036854775808"); // ll min
 
   // Min Width Tests.