Is your feature request related to a problem? Please describe.
I'm working on a make project (meaning my project natures are C Nature, C++ Nature, CDT Make Nature) which uses Javas JNI. This means that code/problem detection (however its proper name is) only works correctly if %JAVA_HOME%/include is added to the project properties under C/C++ Include Paths and Symbols.
However that only works if the absolute path is specified, neither ${JAVA_HOME} or $JAVA_HOME% works.

Describe the solution you'd like
For relative paths using an env variable from the system to get resolved properly. In other words that any variables are resolved against system env variables before trying to be used as an include path.

It seems this is already possible when using a project managed by CDT and not using make, however this is unfortunately not an option for us.

Describe alternatives you've considered
Using the absoluth path is not possible, since any of our devs might have their JDK in a different place with a slightly different minor/patch version.

Additional context
n/a