Packaging+GitLab CI: Dist tarball updates.

Ninja keeps track of its built files in .ninja_log, so if you copy a
pre-built target into a fresh build directory, Ninja will ignore and
overwrite it. This includes the tarball generated by the 'dist' target.

In get-export-release.sh, check for a preexisting tarball and preserve
it by default. This lets us pass the dist tarball from one GitLab CI
stage to other stages without recreating it. It's also arguably the
right thing to do in general, since we record and publish the tarball
hashes for each release and different contents for the same filename can
cause confusion.

Move the dist tarball to the build directory in .gitlab-ci.yml, and add
a note about using the tarball exclusively.

.gitlab-ci.yml

@@ -62,11 +62,14 @@ variables:
 .build-rpm:
   extends: .build
   before_script:
+    # It might make sense to set "GIT_STRATEGY: none" and build from
+    # the tarball.
     - git config --global user.email "you@example.com"
     - git config --global user.name "Your Name"
     - mkdir build
     - cd build
     - perl ../tools/make-version.pl --set-release
+    - mv -v ../wireshark-*.tar.* .
   artifacts:
     paths:
       - build/packaging/rpm/RPMS

packaging/source/git-export-release.sh.in

@@ -19,7 +19,7 @@
 #
 # SPDX-License-Identifier: GPL-2.0-or-later
 
-set -e
+set -e -u -o pipefail
 
 DESTDIR=.
 
@@ -35,10 +35,15 @@ shift $(( OPTIND - 1 ))
 # or 3.4.5-67-gabcd4321
 # By default the version from make-version.pl + CMake is used.
 VERSION=@VERSION@
-if test -n "$1"; then
+if test -n "${1-}"; then
     VERSION="$1"
 fi
 
+if [ -f "${DESTDIR}/wireshark-$VERSION.tar.xz" ] ; then
+    echo "${DESTDIR}/wireshark-$VERSION.tar.xz exists."
+    exit 0
+fi
+
 STASH_POP=false
 XZ_OPTS=
 
@@ -49,7 +54,7 @@ if ! git diff-index --quiet HEAD ; then
     STASH_POP=true
 fi
 
-echo "Creating wireshark-$VERSION.tar.xz"
+echo "Creating ${DESTDIR}/wireshark-$VERSION.tar.xz"
 
 echo . | xz --threads=0 > /dev/null 2>&1 && XZ_OPTS=--threads=0