[PATCH v3] CI: select CC based on CC_PACKAGE (again)

Fix a regression in 707d2f2fe86 (CI: use "$runs_on_pool", not "$jobname" to select packages & config, 2021-11-23).

In that commit I changed CC=gcc from CC=gcc-9, but on OSX the "gcc" in $PATH points to clang, we need to use gcc-9 instead. Likewise for the linux-gcc job CC=gcc-8 was changed to the implicit CC=gcc, which would select GCC 9.4.0 instead of GCC 8.4.0.

Furthermore in 25715419bf4 (CI: don't run "make test" twice in one job, 2021-11-23) when the "linux-TEST-vars" job was split off from "linux-gcc" the "cc_package: gcc-8" line was copied along with it, so its "cc_package" line wasn't working as intended either.

As a table, this is what's changed by this commit, i.e. it only affects the linux-gcc, linux-TEST-vars and osx-gcc jobs:

	|-------------------+-----------+-------------------+-------+-------|
	| jobname           | vector.cc | vector.cc_package | old   | new   |
	|-------------------+-----------+-------------------+-------+-------|
	| linux-clang       | clang     | -                 | clang | clang |
	| linux-sha256      | clang     | -                 | clang | clang |
	| linux-gcc         | gcc       | gcc-8             | gcc   | gcc-8 |
	| osx-clang         | clang     | -                 | clang | clang |
	| osx-gcc           | gcc       | gcc-9             | clang | gcc-9 |
	| linux-gcc-default | gcc       | -                 | gcc   | gcc   |
	| linux-TEST-vars   | gcc       | gcc-8             | gcc   | gcc-8 |
	|-------------------+-----------+-------------------+-------+-------|

Reported-by: Carlo Arenas <carenas@gmail.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

I just dropped the linux-TEST-vars change from the v2 in lieu of trying to get the wording in the commit message right.

Range-diff against v2:
1:  92acf9420a9 ! 1:  8b3444ecc87 CI: select CC based on CC_PACKAGE (again)
    @@ Commit message
         Furthermore in 25715419bf4 (CI: don't run "make test" twice in one
         job, 2021-11-23) when the "linux-TEST-vars" job was split off from
         "linux-gcc" the "cc_package: gcc-8" line was copied along with
    -    it.
    -
    -    That wasn't a bug per-se, as that "make test" would have run under GCC
    -    8 before the split into two jobs, but the point of selecting different
    -    compiler for these jobs is to get better coverage, and to narrow down
    -    any issues with a given compiler to the job that runs it. Since the
    -    "linux-TEST-vars" job is already special in other ways (in running
    -    with various GIT_TEST_* variables), and we've got the "linux-gcc" job
    -    covering gcc-8 let's have it used the default system compiler instead.
    +    it, so its "cc_package" line wasn't working as intended either.
    +
    +    As a table, this is what's changed by this commit, i.e. it only
    +    affects the linux-gcc, linux-TEST-vars and osx-gcc jobs:
    +
    +            |-------------------+-----------+-------------------+-------+-------|
    +            | jobname           | vector.cc | vector.cc_package | old   | new   |
    +            |-------------------+-----------+-------------------+-------+-------|
    +            | linux-clang       | clang     | -                 | clang | clang |
    +            | linux-sha256      | clang     | -                 | clang | clang |
    +            | linux-gcc         | gcc       | gcc-8             | gcc   | gcc-8 |
    +            | osx-clang         | clang     | -                 | clang | clang |
    +            | osx-gcc           | gcc       | gcc-9             | clang | gcc-9 |
    +            | linux-gcc-default | gcc       | -                 | gcc   | gcc   |
    +            | linux-TEST-vars   | gcc       | gcc-8             | gcc   | gcc-8 |
    +            |-------------------+-----------+-------------------+-------+-------|
     
         Reported-by: Carlo Arenas <carenas@gmail.com>
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
    - ## .github/workflows/main.yml ##
    -@@ .github/workflows/main.yml: jobs:
    -           - jobname: linux-TEST-vars
    -             cc: gcc
    -             os: ubuntu
    --            cc_package: gcc-8
    -             pool: ubuntu-latest
    -           - jobname: osx-clang
    -             cc: clang
    -
      ## ci/lib.sh ##
     @@ ci/lib.sh: then
      	test macos != "$CI_OS_NAME" || CI_OS_NAME=osx

 ci/lib.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)