travis-ci: use 'set -x' for the commands under 'su' in the 32 bit Linux build

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

ci/run-linux32-build.sh

@@ -26,6 +26,7 @@ test -z $HOST_UID || (CI_USER="ci" && useradd -u $HOST_UID $CI_USER) &&
 
 # Build and test
 linux32 --32bit i386 su -m -l $CI_USER -c '
+    set -x &&
     cd /usr/src/git &&
     ln -s /tmp/travis-cache/.prove t/.prove &&
     make --jobs=2 &&