automation: allow doing hypervisor only builds

For things like randconfig there's no need to do a full Xen build, a
hypervisor build only will be much faster and will achieve the same
level of testing, as randconfig only changes the hypervisor build
options.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>
Acked-by: Doug Goldstein <cardoe@cardoe.com>

automation/scripts/build

@@ -11,6 +11,7 @@ cc-ver()
 # random config or default config
 if [[ "${RANDCONFIG}" == "y" ]]; then
     make -j$(nproc) -C xen KCONFIG_ALLCONFIG=tools/kconfig/allrandom.config randconfig
+    hypervisor_only="y"
 else
     make -j$(nproc) -C xen defconfig
 fi
@@ -45,16 +46,27 @@ if [[ "${CC}" == "gcc" && `cc-ver` -lt 0x040600 ]]; then
     cfgargs+=("--with-system-seabios=/bin/false")
 fi
 
-./configure "${cfgargs[@]}"
-
-make -j$(nproc) dist
+if [[ "${hypervisor_only}" == "y" ]]; then
+    make -j$(nproc) xen
+else
+    ./configure "${cfgargs[@]}"
+    make -j$(nproc) dist
+fi
 
 # Extract artifacts to avoid getting rewritten by customised builds
 cp xen/.config xen-config
 mkdir binaries
 if [[ "${XEN_TARGET_ARCH}" != "x86_32" ]]; then
     cp xen/xen binaries/xen
-    cp -r dist binaries/
+    if [[ "${hypervisor_only}" != "y" ]]; then
+        cp -r dist binaries/
+    fi
+fi
+
+if [[ "${hypervisor_only}" == "y" ]]; then
+    # If we are build testing a specific Kconfig exit now, there's no point in
+    # testing all the possible configs.
+    exit 0
 fi
 
 # Build all the configs we care about