Use <config.h>, not "config.h", per autoconf documentation.
* Makefile.cfg (local-checks-to-skip) [sc_require_config_h]: Enable.
* .x-sc_require_config_h: New file, to list exempted files.
* Makefile.am (EXTRA_DIST): Add .x-sc_require_config_h.
* src/bridge.c, src/bridge.h, src/qemu_conf.c, src/qemu_conf.h,
src/qemu_driver.c, src/qemu_driver.h, src/test.c: Disable more
of qemu if configured --without-qemu.