ci: Split clang into separate script, run it in CoreOS CI

Let's do a build with clang as a cleanly separate context
instead of serially; and also do it unconditionally.  This
is prep for turning on more `-Werror` flow in both cases,
and also using clang `scan-build` in CI.

.cci.jenkinsfile

@@ -48,7 +48,16 @@ unit: {
         MAKE_JOBS=${n} CARGO_BUILD_JOBS=${n} ci/unit.sh
       """)
   }
-}}
+},
+clang: {
+  // Build with clang/clang++
+  def n = 5
+  cosaPod(buildroot: true, runAsUser: 0, memory: "2Gi", cpu: "${n}") {
+      checkout scm
+      shwrap("ci/clang-build-check.sh")
+  }
+}
+}
 
 stage("Test") {
 parallel insttests: {

ci/build-check.sh

@@ -14,26 +14,3 @@ export PATH="$HOME/.cargo/bin:$PATH"
 ${dn}/build.sh
 make check
 make install
-
-# And now a clang build with -Werror turned on. We can't do this with gcc (in
-# build.sh) because it doesn't support -Wno-error=macro-redefined, (and neither
-# does clang on CentOS). Anyway, all we want is at least one clang run.
-if test -x /usr/bin/clang; then
-  if grep -q -e 'static inline.*_GLIB_AUTOPTR_LIST_FUNC_NAME' /usr/include/glib-2.0/glib/gmacros.h; then
-      echo 'Skipping clang check, see https://bugzilla.gnome.org/show_bug.cgi?id=796346'
-  else
-  # Except unused-command-line-argument:
-  #   error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened    -cc1' [-Werror,-Wunused-command-line-argument]
-  # Except for macro-redefined:
-  #   /usr/include/python2.7/pyconfig-64.h:1199:9: error: '_POSIX_C_SOURCE' macro redefined
-  # Except for deprecated-declarations: libdnf python bindings uses deprecated
-  # functions
-  export CFLAGS="-Wall -Werror -Wno-error=deprecated-declarations -Wno-error=macro-redefined -Wno-error=unused-command-line-argument ${CFLAGS:-}"
-  export CC=clang
-  git clean -dfx && git submodule foreach git clean -dfx
-  # XXX: --disable-introspection because right now we're always building the
-  # introspection bits with gcc, which doesn't understand some of the flags
-  # above (see Makefile-lib.am)
-  build ${CONFIGOPTS:-} --disable-introspection
-  fi
-fi

ci/clang-build-check.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/bash
+# Install build dependencies, run unit tests and installed tests.
+
+# This script is what Prow runs.
+
+set -xeuo pipefail
+
+dn=$(dirname $0)
+. ${dn}/libbuild.sh
+
+# add cargo's directory to the PATH like we do in CoreOS CI
+export PATH="$HOME/.cargo/bin:$PATH"
+
+export CC=clang CXX=clang++
+${dn}/build.sh
+make check