We already have virAsprintf, so picking a similar name helps for
seeing a similar purpose.  Furthermore, the prefix V before printf
generally implies 'va_list', even though this variant was '...', and
the old name got in the way of adding a new va_list version.

global rename performed with:

$ git grep -l virBufferVSprintf \
  | xargs -L1 sed -i 's/virBufferVSprintf/virBufferAsprintf/g'

then revert the changes in ChangeLog-old.

And from all related macros and functions.

* src/util/sysinfo.h (virSysinfoFormat): New prototype.
* src/conf/domain_conf.c (virDomainSysinfoDefFormat): Move guts...
* src/util/sysinfo.c (virSysinfoFormat): ...into new function.
* src/libvirt_private.syms: Export it.

* src/util/sysinfo.c (virSysinfoRead): Use virCommand instead of
virExec.

* src/util/sysinfo.c: Indentation and () fixups.

* docs/schemas/domain.rng (sysinfo-system-name): Also allow
family.
* src/util/sysinfo.h (struct _virSysinfoDef): Add system_family.
* src/conf/domain_conf.c (virSysinfoParseXML)
(virDomainSysinfoDefFormat): Support it.
* src/util/sysinfo.c (virSysinfoDefFree, virSysinfoRead): Likewise.
* src/qemu/qemu_conf.c (qemuBuildSmbiosSystemStr): Likewise.
* tests/qemuxml2argvdata/qemuxml2argv-smbios.xml: Adjust test.
* tests/qemuxml2argvdata/qemuxml2argv-smbios.args: Likewise.

Move existing routines about virSysinfoDef to an util module,
add a new entry point virSysinfoRead() to read the host values
with dmidecode

* src/conf/domain_conf.c src/conf/domain_conf.h src/util/sysinfo.c
  src/util/sysinfo.h: move to a new module, add virSysinfoRead()
* src/Makefile.am: handle the new module build
* src/libvirt_private.syms: new internal symbols
* include/libvirt/virterror.h src/util/virterror.c: defined a new
  error code for that module
* po/POTFILES.in: add new file for translations