Merge branch 'jk/dev-build-format-security'

Earlier we added "-Wformat-security" to developer builds, assuming that "-Wall" (which includes "-Wformat" which in turn is required to use "-Wformat-security") is always in effect. This is not true when config.mak.autogen is in use, unfortunately. This has been fixed by unconditionally adding "-Wall" to developer builds. * jk/dev-build-format-security: config.mak.dev: add -Wall, primarily for -Wformat, to help autoconf users