[MNG-8402] System properties can take precedence over builtin expressions

**[Guillaume Nodet](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=gnt)** opened **[MNG-8402](https://issues.apache.org/jira/browse/MNG-8402?redirect=false)** and commented


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**Affects:** 4.0.0-beta-5

**Remote Links:**
- [GitHub Pull Request #1947
](https://github.com/apache/maven/pull/1947)

**Backported to:** [4.0.0-rc-2](https://github.com/apache/maven/milestone/27?closed=1)
