since 4.11 pci_enable_msi_exact is no more available and fail with :

spec-sw/kernel/spec-pci.c: In function 'spec_probe':
spec-sw/kernel/spec-pci.c:225:9: error: implicit declaration of function 'pci_enable_msi_exact'; did you mean 'pci_enable_msix_exact'? [-Werror=implicit-function-declaration]
   ret = pci_enable_msi_exact(pdev, 1);
         ^~~~~~~~~~~~~~~~~~~~
         pci_enable_msix_exact
cc1: some warnings being treated as errors
make[5]: *** [/usr/src/linux-headers-4.18.0-2-common/scripts/Makefile.build:323: spec-sw/kernel/spec-pci.o] Error 1
make[4]: *** [/usr/src/linux-headers-4.18.0-2-common/Makefile:1531: _module_spec-sw/kernel] Error 2
make[3]: *** [Makefile:146: sub-make] Error 2
make[2]: *** [Makefile:8: all] Error 2
make[2]: Leaving directory '/usr/src/linux-headers-4.18.0-2-amd64'
make[1]: *** [Makefile:20: all] Error 2
make[1]: Leaving directory 'spec-sw/kernel'
make: *** [Makefile:28: kernel] Error 2

This patch add preprocessor case to detect kernel version.
For kernel > 4.11 pci_alloc_irq_vectors is use instead of pci_enable_msi_exact
and pci_free_irq_vectors instead of pci_disable_msi.
Signed-off-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@trabucayre.com>