configure: Quote the configure args printed in config.log

Use the same mechanism we use for printing the configure command
line to config-host.mak to print it to config.log. This fixes a
bug where the config.log version didn't quote arguments with spaces.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>