[PATCH v3 0/4] ci: detect more warnings via `-Og`

Hi,

this is the third version of this patch series that adapts one of our CI jobs to compile with `-Og` for improved coverage of warnings.

Changes compared to v2:

  - Typo fixes for commit messages.

  - Replaced the `O` variable with `CFLAGS_APPEND`. If that isn't
    palatable to folks then I'll drop this altogether and will inline it
    into the CI script, duplicating the default CFLAGS there.

  - Start compiling with V=1 so that the change can actually be seen. It
    also shouldn't clutter the job output too much given that the build
    is in a collapsible section on both GitHub and GitLab.

Patrick

Patrick Steinhardt (4):
  ci: fix check for Ubuntu 20.04
  Makefile: add ability to append to CFLAGS and LDFLAGS
  ci: compile code with V=1
  ci: compile "linux-gcc-default" job with -Og

 Makefile                  |  2 ++
 ci/lib.sh                 |  2 +-
 ci/run-build-and-tests.sh | 11 ++++++++++-
 3 files changed, 13 insertions(+), 2 deletions(-)

Range-diff against v2:
1:  f91004a438 = 1:  70fa755b4f ci: fix check for Ubuntu 20.04
-:  ---------- > 2:  d68539834f Makefile: add ability to append to CFLAGS and LDFLAGS
-:  ---------- > 3:  a3dfb7092a ci: compile code with V=1
2:  bdf0e40a77 ! 4:  c7b5b62d9c ci: compile "linux-gcc-default" job with -Og
    @@ Commit message
     
         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 but puzzling because it was
    +    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
    @@ Commit message
         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 loose coverage for
    +    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
    @@ Commit message
     
         Signed-off-by: Patrick Steinhardt <ps@pks.im>
     
    - ## Makefile ##
    -@@ Makefile: endif
    - # tweaked by config.* below as well as the command-line, both of
    - # which'll override these defaults.
    - # Older versions of GCC may require adding "-std=gnu99" at the end.
    --CFLAGS = -g -O2 -Wall
    -+O ?= 2
    -+CFLAGS = -g -O$(O) -Wall
    - LDFLAGS =
    - CC_LD_DYNPATH = -Wl,-rpath,
    - BASIC_CFLAGS = -I.
    -
      ## ci/run-build-and-tests.sh ##
     @@ ci/run-build-and-tests.sh: esac
      run_tests=t
    @@ ci/run-build-and-tests.sh: esac
     +	# `-O2` will mask others. We thus use `-Og` here just so that we have
     +	# at least one job with a different optimization level so that we can
     +	# overall surface more warnings.
    -+	export O=g
    ++	export CFLAGS_APPEND=-Og
     +	;;
      linux-gcc)
      	export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main