[PATCH v4 2/2] ci: compile "linux-gcc-default" job with -Og

We have recently noticed that our CI does not always notice variables that may be used uninitialized. While it is expected that compiler warnings aren't perfect, this one was a bit puzzling because it was rather obvious that the variable can be uninitialized.

Many compiler warnings unfortunately depend on the optimization level used by the compiler. While `-O0` for example will disable a lot of warnings altogether because optimization passes go away, `-O2`, which is our default optimization level used in CI, may optimize specific code away or even double down on undefined behaviour. Interestingly, this specific instance that triggered the investigation does get noted by GCC when using `-Og`.

While we could adapt all jobs to compile with `-Og` now, that would potentially mask other warnings that only get diagnosed with `-O2`. Instead, adapt the "linux-gcc-default" job to compile with `-Og`. This job is chosen because it uses the "ubuntu:latest" image and should thus have a comparatively recent compiler toolchain, and because we have other jobs that use "ubuntu:latest" so that we do not lose coverage for warnings diagnosed only on `-O2` level.

To make it easier to set up the optimization level in our CI, add support in our Makefile to specify the level via an environment variable.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
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 ci/run-build-and-tests.sh | 9 +++++++++
 1 file changed, 9 insertions(+)