appveyor build bots run out of memory

[gnzlbg]

All 3 out of 4 appveyor build bots currently run out of memory.

We should try to find a way to minimize memory consumption in the ci/run.sh file.

A good start would be to switch to:

• single job: --jobs 1 / CARGO_BUILD_JOBS=1
• single code-gen unit: RUSTFLAGS="-C codegen-units=1"
• no debug info RUSTFLAGS="-C debuginfo=0"

[gnzlbg]

Maybe switch incremental compilation off, does CARGO_INCREMENTAL=0 still works? cc @michaelwoerister

[michaelwoerister]

CARGO_INCREMENTAL=0 still works, yes.

[gnzlbg]

This has been fixed in #62 by using --cfg ... to only enable a subset of the tests on each cargo test run (which now is run 4 consecutive times).

Basically we slice the testsuite into 4 chunks, so that compiling it uses much less memory.