CircleCI: do not add Debian-specific parameter when invoking setup.py

Runners on https://circleci.com/ use a custom version of Python without
Debian-specific patches which added option --install-layout=deb. This
leads to the following error:

    error: option --install-layout not recognized

Fix this by creating a new environment variable dedicated to detect
CircleCI platform.

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
Acked-by: James Carter <jwcart2@gmail.com>

.circleci/config.yml

@@ -19,6 +19,7 @@ jobs:
         name: Setup environment variables
         command: |
           echo 'export DESTDIR=$HOME/destdir' >> "$BASH_ENV"
+          echo 'export IS_CIRCLE_CI=1' >> "$BASH_ENV"
 
     # Download and install refpolicy headers for sepolgen tests
     - run:

scripts/run-scan-build

@@ -24,7 +24,7 @@ export PATH="$DESTDIR/usr/sbin:$DESTDIR/usr/bin:$DESTDIR/sbin:$DESTDIR/bin:$PATH
 export PYTHONPATH="$DESTDIR$(${PYTHON:-python3} -c "from distutils.sysconfig import *;print(get_python_lib(prefix='/usr'))")"
 export RUBYLIB="$DESTDIR/$(${RUBY:-ruby} -e 'puts RbConfig::CONFIG["vendorlibdir"]'):$DESTDIR/$(${RUBY:-ruby} -e 'puts RbConfig::CONFIG["vendorarchdir"]')"
 
-if [ -f /etc/debian_version ]; then
+if [ -f /etc/debian_version ] && [ -z "${IS_CIRCLE_CI:-}" ] ; then
     export PYTHON_SETUP_ARGS='--install-layout=deb'
 fi