RFR: 8302667: Improve message format when failing to load symbols or libraries

[Julian Waters]

DLL_ERROR4 is a macro expanding to an error message when a failure to load a generic item (shared libraries or an exported symbol from said libraries for example) occurs. "Error: loading:" is not a very pretty message, so this small change results in "Error: Failed to load %s" instead, which looks better and also means the message makes more sense if we want to append a reason behind as well, such as "Error: Failed to load libjvm.so because xxx"

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Commit messages:
 - Error: Failed to load

Changes: https://git.openjdk.org/jdk/pull/12596/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12596&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302667
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12596.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12596/head:pull/12596

PR: https://git.openjdk.org/jdk/pull/12596