tools: rename xen-tools/libs.h file to common-macros.h

In order to better reflect the contents of the header and to make it
more appropriate to use it for different runtime environments like
programs, libraries, and firmware, rename the libs.h include file to
common-macros.h. Additionally add a comment pointing out the need to be
self-contained.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> # tools/python/xen/lowlevel/xc/xc.c
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

tools/python/xen/lowlevel/xc/xc.c

@@ -22,7 +22,7 @@
 #include <xen/hvm/hvm_info_table.h>
 #include <xen/hvm/params.h>
 
-#include <xen-tools/libs.h>
+#include <xen-tools/common-macros.h>
 
 /* Needed for Python versions earlier than 2.3. */
 #ifndef PyMODINIT_FUNC