RFR: 8283287: ClassLoader.c cleanups [v5]

[Tyler Steele]

On Fri, 18 Mar 2022 15:40:09 GMT, Tyler Steele <duke at openjdk.java.net> wrote:

>> As mentioned in the issue, I'd like to perform the following tidying on ClassLoader.c
>> 
>> - Alphabetize includes.
>> - Replace 'if (ptr == 0)' with 'if (ptr == NULL)'.
>> - Replace 'return 0' with 'return NULL'.
>
> Tyler Steele has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Makes requested readability changes

Made some additional readability changes that were requested after #7829 closed. They felt appropriate here since it's already a cleanup PR.

All changes complete. Please sponsor when ready.

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PR: https://git.openjdk.java.net/jdk/pull/7846