[libc][obvious] fix errno for 32 bit long test

[michaelrj]

Summary

one of the tests in StrtolTest.h is intended to detect that 32 bit longs
are handled correctly, but it wasn't using the correct value for errno
causing failures.

libc/test/src/stdlib/StrtolTest.h

void CleanBaseTenDecode(FunctionT func) {
     ASSERT_EQ(func(big_number, &str_end, 10), ReturnT(1234567890));
     ASSERT_EQ(errno, 0);
     EXPECT_EQ(str_end - big_number, ptrdiff_t(10));
 
     // This number is larger than 2^32, meaning that if long is only 32 bits
     // wide, strtol will return LONG_MAX.
     const char *bigger_number = "12345678900";
     errno = 0;
-    ASSERT_EQ(func(bigger_number, &str_end, 10),
-              ((sizeof(ReturnT) < 8) ? T_MAX : ReturnT(12345678900)));
+    if constexpr (sizeof(ReturnT) < 8) {
+      ASSERT_EQ(func(bigger_number, &str_end, 10), T_MAX);
+      ASSERT_EQ(errno, ERANGE);
+    } else {
+      ASSERT_EQ(func(bigger_number, &str_end, 10), ReturnT(12345678900));
       ASSERT_EQ(errno, 0);
+    }
     EXPECT_EQ(str_end - bigger_number, ptrdiff_t(11));
 
     const char *too_big_number = "123456789012345678901";
     errno = 0;
     ASSERT_EQ(func(too_big_number, &str_end, 10), T_MAX);
     ASSERT_EQ(errno, ERANGE);
     EXPECT_EQ(str_end - too_big_number, ptrdiff_t(21));