Fix how the arguments are passed to GN's bootstrap.py

I don't know why, but previously it was failing only on aarch64.

chromium.spec

@@ -1267,7 +1267,7 @@ if python2 -c 'import google ; print google.__path__' 2> /dev/null ; then \
     exit 1 ; \
 fi
 
-tools/gn/bootstrap/bootstrap.py -v "$CHROMIUM_CORE_GN_DEFINES $CHROMIUM_BROWSER_GN_DEFINES"
+tools/gn/bootstrap/bootstrap.py -v --no-clean --gn-gen-args="$CHROMIUM_CORE_GN_DEFINES $CHROMIUM_BROWSER_GN_DEFINES"
 %{builddir}/gn --script-executable=/usr/bin/python2 gen --args="$CHROMIUM_CORE_GN_DEFINES $CHROMIUM_BROWSER_GN_DEFINES" %{builddir}
 
 %if %{freeworld}