ci: make MAKEFLAGS available inside the Docker container in the Linux32 job

Once upon a time we ran 'make --jobs=2 ...' to build Git, its
documentation, or to apply Coccinelle semantic patches.  Then commit
eaa62291ff (ci: inherit --jobs via MAKEFLAGS in run-build-and-tests,
2019-01-27) came along, and started using the MAKEFLAGS environment
variable to centralize setting the number of parallel jobs in
'ci/libs.sh'.  Alas, it forgot to update 'ci/run-linux32-docker.sh' to
make MAKEFLAGS available inside the Docker container running the 32
bit Linux job, and, consequently, since then that job builds Git
sequentially, and it ignores any Makefile knobs that we might set in
MAKEFLAGS (though we don't set any for the 32 bit Linux job at the
moment).

So update the 'docker run' invocation in 'ci/run-linux32-docker.sh' to
make MAKEFLAGS available inside the Docker container as well.  Set
CC=gcc for the 32 bit Linux job, because that's the compiler installed
in the 32 bit Linux Docker image that we use (Travis CI nowadays sets
CC=clang by default, but clang is not installed in this image).

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ci/lib.sh

@@ -192,6 +192,9 @@ osx-clang|osx-gcc)
 GIT_TEST_GETTEXT_POISON)
 	export GIT_TEST_GETTEXT_POISON=true
 	;;
+Linux32)
+	CC=gcc
+	;;
 esac
 
 MAKEFLAGS="$MAKEFLAGS CC=${CC:-cc}"

ci/run-linux32-docker.sh

@@ -20,6 +20,7 @@ docker run \
 	--env GIT_PROVE_OPTS \
 	--env GIT_TEST_OPTS \
 	--env GIT_TEST_CLONE_2GB \
+	--env MAKEFLAGS \
 	--env cache_dir="$container_cache_dir" \
 	--volume "${PWD}:/usr/src/git" \
 	--volume "$cache_dir:$container_cache_dir" \