Enable maintainer mode after autogen.sh

As documented in autogen.des, this is what we should use for development
and it should encompass continuous integration. Until autogen.sh goes
away we need to explicitly enable maintainer mode at configure time.

Two thirds of our CI setup rely on autogen.des today.

Better diff with the --word-diff option.

.travis.yml

@@ -24,7 +24,7 @@ jobs:
             - libpcre3-dev
       before_script:
         - ./autogen.sh
-        - ./configure --with-unwind
+        - ./configure --enable-maintainer-mode --with-unwind
       script: &script-common
         - |
           if [[ "$TRAVIS_PULL_REQUEST" != "false" ]]; then
@@ -38,13 +38,13 @@ jobs:
       compiler: gcc
       before_script:
         - ./autogen.sh
-        - ./configure
+        - ./configure --enable-maintainer-mode
     - <<: *test-linux
       compiler: gcc
       arch: arm64
       before_script:
         - ./autogen.sh
-        - ./configure
+        - ./configure --enable-maintainer-mode
     - <<: *test-linux
       env: WITNESS=1
       script: make -j8 witness
@@ -72,7 +72,7 @@ jobs:
           export UBSAN_OPTIONS=halt_on_error=1,print_stacktrace=1,use_sigaltstack=0,suppressions=$(pwd)/tools/ubsan.suppr
           export CC=clang-9
         - ./autogen.sh
-        - ./configure --with-unwind --enable-developer-warnings --enable-debugging-symbols --disable-stack-protector --with-persistent-storage --enable-asan --enable-ubsan
+        - ./configure --enable-maintainer-mode --with-unwind --enable-developer-warnings --enable-debugging-symbols --disable-stack-protector --with-persistent-storage --enable-asan --enable-ubsan
     - stage: test
       os: osx
       osx_image: xcode11.4
@@ -86,8 +86,8 @@ jobs:
           update: true
       before_script:
         - export PATH="/usr/local/opt/sphinx-doc/bin:$PATH"
-        - autoreconf -i
-        - ./configure
+        - ./autogen.sh
+        - ./configure --enable-maintainer-mode
       script: *script-common
     - <<: *test-linux
       stage: coverity
@@ -102,7 +102,7 @@ jobs:
         - export PATH=$PATH:$(echo $(pwd)/cov-analysis-*/bin)
       script:
         - ./autogen.sh
-        - ./configure --with-unwind
+        - ./configure --enable-maintainer-mode --with-unwind
         - cov-build --dir cov-int make
         - tar cfz varnish.tgz cov-int
         - curl --form token="$COVTOKEN"

tools/coverity-run

@@ -37,7 +37,7 @@ test "`basename $PWD`" = "devscripts" && cd ..
 
 make distclean || true
 test -f configure || ./autogen.sh
-./configure
+./configure --enable-maintainer-mode
 
 cov-build --dir cov-int make