Building with the attached random configuration file,
arch/x86/built-in.o: In function `early_put_chars':
boot.c:(.init.text+0x150): undefined reference to `write_pci_config'
boot.c:(.init.text+0x169): undefined reference to `early_pci_allowed'
boot.c:(.init.text+0x18e): undefined reference to `read_pci_config'
boot.c:(.init.text+0x1aa): undefined reference to `read_pci_config'
boot.c:(.init.text+0x1d6): undefined reference to `read_pci_config_byte'
boot.c:(.init.text+0x1f9): undefined reference to `read_pci_config_byte'
boot.c:(.init.text+0x218): undefined reference to `read_pci_config_byte'
boot.c:(.init.text+0x232): undefined reference to `read_pci_config_byte'
boot.c:(.init.text+0x24c): undefined reference to `read_pci_config'
boot.c:(.init.text+0x29c): undefined reference to `read_pci_config_byte'
boot.c:(.init.text+0x30d): undefined reference to `write_pci_config'
boot.c:(.init.text+0x336): undefined reference to `read_pci_config'
arch/x86/built-in.o: In function `lguest_init':
(.init.text+0x621): undefined reference to `pcibios_enable_irq'
arch/x86/built-in.o: In function `lguest_init':
(.init.text+0x62b): undefined reference to `pcibios_disable_irq'
arch/x86/built-in.o: In function `set_cfg_window':
boot.c:(.text.unlikely+0x27): undefined reference to `write_pci_config_byte'
boot.c:(.text.unlikely+0x4c): undefined reference to `write_pci_config'
boot.c:(.text.unlikely+0x61): undefined reference to `write_pci_config'
make: *** [vmlinux] Error 1