Disable leak detection if debug symbols are unavailable

There just doesn't seem to be any way to make this work right now, so
handle dbgsym packages installation failure and disable leak detection
in this case.

Hopefully ddebs.ubuntu.com repository will be updated in the future,
allowing this to work again.

build/tools/before_install.sh

@@ -43,7 +43,7 @@ case $(uname -s) in
                 wget -O - http://ddebs.ubuntu.com/dbgsym-release-key.asc | $SUDO apt-key add -
 
                 # Install the symbols to allow LSAN suppression list to work.
-                pkg_install='libfontconfig1-dbgsym libglib2.0-0-dbgsym libgtk-3-0-dbgsym libatk-bridge2.0-0-dbgsym'
+                dbgsym_pkgs='libfontconfig1-dbgsym libglib2.0-0-dbgsym libgtk-3-0-dbgsym libatk-bridge2.0-0-dbgsym'
             fi
 
             run_apt update
@@ -85,7 +85,18 @@ case $(uname -s) in
                 fi
             done
 
-            run_apt install -y $pkg_install
+            if ! run_apt install -y $pkg_install $dbgsym_pkgs; then
+                if [ -z "$dbgsym_pkgs" ]; then
+                    exit $?
+                fi
+
+                # Retry without dbgsym packages that currently fail to install
+                # under Ubuntu Focal (20.04).
+                echo 'Installing with dbgsym packages failed, retrying without...'
+                run_apt install -y $pkg_install
+            else
+                touch wx_dbgsym_available
+            fi
         fi
         ;;