rpm: include kernel headers in modules.img for VM

Distributing kernel-devel built for dom0 to VMs is major PITA, including
problems like copying between different build environments, inability to
install it in Debian etc.
Lets include kernel headers there by default, without any additional
package needed.

Fixes QubesOS/qubes-issues#2692

Makefile.builder

 ifeq ($(PACKAGE_SET),dom0)
 RPM_SPEC_FILES := kernel.spec
-else ifeq ($(PACKAGE_SET),vm)
-
-ifdef UPDATE_REPO
-# If DIST_DOM0 defined, copy kernel-devel from there
-ifneq ($(DIST_DOM0),)
-# Include kernel-devel packages in VM repo - dummy spec file
-RPM_SPEC_FILES := kernel-devel.spec
-OUTPUT_DIR = pkgs/$(DIST_DOM0)
-endif
-endif
-
 endif

kernel.spec

@@ -358,6 +358,11 @@ cp -a %buildroot/lib/modules/%kernelrelease %buildroot%vm_install_dir/modules/
 mkdir -p %buildroot%vm_install_dir/modules/firmware
 cp -a %buildroot/lib/firmware/%kernelrelease %buildroot%vm_install_dir/modules/firmware/
 
+# Include kernel headers for Qubes VM in "/lib/modules" - so kernel-devel
+# package will be unnecessary there, regardless of distribution
+rm -f %buildroot%vm_install_dir/modules/%kernelrelease/build
+cp -a %buildroot/%src_install_dir %buildroot%vm_install_dir/modules/%kernelrelease/build
+
 # remove files that will be auto generated by depmod at rpm -i time
 for i in alias alias.bin ccwmap dep dep.bin ieee1394map inputmap isapnpmap ofmap pcimap seriomap symbols symbols.bin usbmap
 do