Makefile: Add dependency between libvmcp and libutil to fix -j builds

For linking the "libvmcp" example program the "libutil" is required.
Therefore when the "libvmcp" directory is entered in a parallel build
and the "libutil.a" file has not yet been created, a second "libutil"
build is triggered which can then lead to build errors like the following:

 ar: libutil.a: File format not recognized
 ar: libutil.a: No such file or directory
 make[2]: Leaving directory '/builddir/build/BUILD/s390-tools-2.6.0/libutil'
 make[2]: *** [../common.mak:246: libutil.a] Error 1
 make[1]: *** [../common.mak:246: libutil.a] Error 1
 make[1]: *** Waiting for unfinished jobs....
 make[1]: *** [../common.mak:315: ..//libutil/libutil.a] Error 2
 make[1]: Leaving directory '/builddir/build/BUILD/s390-tools-2.6.0/libvmcp'
 make: *** [Makefile:57: libvmcp] Error 2
 make: *** Waiting for unfinished jobs....
ving directory '/builddir/build/BUILD/s390-tools-2.6.0/libutil'
 make: *** [Makefile:57: libutil] Error 2
 error: Bad exit status from /var/tmp/rpm-tmp.wCulxB (%build)

So fix this and add a dependency between libvmcp and libutil.

Signed-off-by: Michael Holzheu <holzheu@linux.ibm.com>
Reviewed-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

common.mak

@@ -343,6 +343,9 @@ $(rootdir)/libvmcp/libvmcp.a: $(rootdir)/libvmcp
 	$(MAKE) -C $(rootdir)/libvmcp/ libvmcp.a
 .PHONY: $(rootdir)/libvmcp
 
+# Dependencies between libraries
+$(rootdir)/libvmcp: $(rootdir)/libutil/libutil.a
+
 $(rootdir)/zipl/boot/data.o:
 	$(MAKE) -C $(rootdir)/zipl/boot/ data.o