support compiler.jvm.target=7

[jvasileff]

With .ceylon/config that includes:

[compiler.jvm]
target=7

and Eclipse on a system that does not have Java 7, I get a single error in the problems view: "The Ceylon Java backend compilation failed".

In the projects settings, "Compiler compliance level" is set to "1.7". Same result for "1.8".

[davidfestal]

@jvasileff I cannot reproduce this. could you provide more details, or an example project ?

[jvasileff]

@davidfestal this went from 100% reproducible (over multiple days/weeks!) to 100% non-reproducible :(

With an error like:

The Ceylon Java backend compilation failed"

it's really hard to know what the precipitating factors are.

I guess we should just fix https://github.com/ceylon/ceylon/issues/6730#issuecomment-261806500 (correct the target=7 config in ceylon-sdk) and see if people complain?