vboxguestdrivers: make sure that do_compile fails when some module failed to build

* otherwise we get the failure from do_install with useless log:
  DEBUG: Executing shell function do_install
  install: cannot stat 'vboxsf.ko': No such file or directory
  WARNING: exit code 1 from a shell command.
* instead of the real issue like 5.1.14 currently has with default linux-yocto
  version:
  CC [M]  qemux86-oe-linux/vboxguestdrivers/5.1.14-r0/vbox_module/vboxsf/lnkops.o
          qemux86-oe-linux/vboxguestdrivers/5.1.14-r0/vbox_module/vboxsf/lnkops.c:93:23: error: 'generic_readlink' undeclared here (not in a function)
     .readlink       = generic_readlink,
                       ^~~~~~~~~~~~~~~~

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>

meta-oe/recipes-support/vboxguestdrivers/vboxguestdrivers_4.3.36.bb

@@ -41,6 +41,10 @@ do_export_sources() {
 # compile and install mount utility
 do_compile_append() {
     oe_runmake 'LD=${CC}' 'LDFLAGS=${LDFLAGS}' -C ${S}/utils
+    if ! [ -e vboxguest.ko -a -e vboxsf.ko -a -e vboxvideo.ko ] ; then
+        echo "ERROR: One of vbox*.ko modules wasn't built"
+        exit 1
+    fi
 }
 
 module_do_install() {

meta-oe/recipes-support/vboxguestdrivers/vboxguestdrivers_5.1.14.bb

@@ -41,6 +41,10 @@ do_export_sources() {
 # compile and install mount utility
 do_compile_append() {
     oe_runmake 'LD=${CC}' 'LDFLAGS=${LDFLAGS}' -C ${S}/utils
+    if ! [ -e vboxguest.ko -a -e vboxsf.ko -a -e vboxvideo.ko ] ; then
+        echo "ERROR: One of vbox*.ko modules wasn't built"
+        exit 1
+    fi
 }
 
 module_do_install() {