[MCOMPILER-537] Inconsistent behaviour when compiler is forked

**[Sebb](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=sebb@apache.org)** opened **[MCOMPILER-537](https://issues.apache.org/jira/browse/MCOMPILER-537?redirect=false)** and commented

Further to MCOMPILER-491, there is another difference between forked and non-forked compiles. Informational messages about deprecation etc are not shown in the forked case.

For example:

$ git clone https://gitbox.apache.org/repos/asf/commons-compress.git --single-branch --branch commons-compress-1.22 --depth 1
$ cd commons-compress
$ mvn clean compile
...
[INFO] --- maven-compiler-plugin:3.10.1:compile (default-compile) @ commons-compress ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 360 source files to /private/tmp/commons-compress/target/classes
[INFO] /private/tmp/commons-compress/src/main/java/org/apache/commons/compress/harmony/pack200/Archive.java: Some input files use or override a deprecated API.
[INFO] /private/tmp/commons-compress/src/main/java/org/apache/commons/compress/harmony/pack200/Archive.java: Recompile with -Xlint:deprecation for details.
[INFO] /private/tmp/commons-compress/src/main/java/org/apache/commons/compress/harmony/unpack200/AttributeLayoutMap.java: Some input files use unchecked or unsafe operations.
[INFO] /private/tmp/commons-compress/src/main/java/org/apache/commons/compress/harmony/unpack200/AttributeLayoutMap.java: Recompile with -Xlint:unchecked for details.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
...
$ mvn clean compile -Dcommons.compiler.fork=true
...[INFO] Compiling 360 source files to /private/tmp/commons-compress/target/classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
...

---

**Issue Links:**
- [MCOMPILER-491](https://issues.apache.org/jira/browse/MCOMPILER-491) testCompile goal doesn't fail the build when encoding error occurs

Reproduce the issue with the two commands shown in the report, using the commons-compress 1.22 example, and compare compiler output for forked and non-forked compilation. Investigate the Maven Compiler Plugin's forked compilation path and MCOMPILER-491 for context; done means informational deprecation and unchecked-operation messages are visible in both modes.

Written by the indexing model from the issue text.