RFR: 8283287: ClassLoader.c cleanups [v3]

[Tyler Steele]

> 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 with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge branch 'master' into ClassLoaderCleanup
 - removes unneeded errno.h
 - Perform minor clean up ClassLoader.c
   
   - Alphabatizes includes.
   - Replaces 'if (ptr == 0)' with 'if (ptr == NULL)'.
   - Replaces 'return 0' with 'return NULL'.

-------------

Changes: https://git.openjdk.java.net/jdk/pull/7846/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7846&range=02
  Stats: 26 lines in 1 file changed: 6 ins; 5 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7846.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7846/head:pull/7846

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