Building with the attached random configuration file,

drivers/xen/platform-pci.c: In function ‘platform_pci_init’:
drivers/xen/platform-pci.c:131:2: error: implicit declaration of
function ‘pci_request_region’ [-Werror=implicit-function-declaration]
  ret = pci_request_region(pdev, 1, DRV_NAME);
  ^
drivers/xen/platform-pci.c:170:2: error: implicit declaration of
function ‘pci_release_region’ [-Werror=implicit-function-declaration]
  pci_release_region(pdev, 0);
  ^
cc1: some warnings being treated as errors
make[2]: *** [drivers/xen/platform-pci.o] Error 1

These warnings appeared too:

warning: (XEN_PVH) selects XEN_PVHVM which has unmet direct
dependencies (HYPERVISOR_GUEST && XEN && PCI && X86_LOCAL_APIC)