conf: don't use virDomainVirtType in struct field

Use of enum types for struct fields is generally avoided since it causes
warnings if the compiler assumes the enum is unsigned. For example

  commit 8e2982b5
  Author: Cole Robinson <crobinso@redhat.com>
  Date:   Tue Jul 24 16:27:54 2018 -0400

    conf: Clean up virDomainDefParseCaps

Introduced a line:

  if ((def->virtType = virDomainVirtTypeFromString(virttype)) < 0) {

which causes a build failure with CLang

  conf/domain_conf.c:19143:65: error: comparison of unsigned enum expression < 0 is always false [-Werror,-Wtautological-compare]

as the compiler is free to optimize away the "< 0" check due to the
assumption that the enum type is unsigned and always in range.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

src/conf/domain_conf.c

@@ -15075,7 +15075,7 @@ virDomainVideoDefaultRAM(const virDomainDef *def,
 int
 virDomainVideoDefaultType(const virDomainDef *def)
 {
-    switch (def->virtType) {
+    switch ((virDomainVirtType)def->virtType) {
     case VIR_DOMAIN_VIRT_TEST:
     case VIR_DOMAIN_VIRT_XEN:
         if (def->os.type == VIR_DOMAIN_OSTYPE_XEN ||

src/conf/domain_conf.h

@@ -2386,7 +2386,7 @@ struct _virDomainVirtioOptions {
 typedef struct _virDomainDef virDomainDef;
 typedef virDomainDef *virDomainDefPtr;
 struct _virDomainDef {
-    virDomainVirtType virtType;
+    int virtType; /* enum virDomainVirtType */
     int id;
     unsigned char uuid[VIR_UUID_BUFLEN];
 

src/qemu/qemu_command.c

@@ -7163,7 +7163,7 @@ qemuBuildMachineCommandLine(virCommandPtr cmd,
     virCommandAddArg(cmd, "-machine");
     virBufferAdd(&buf, def->os.machine, -1);
 
-    switch (def->virtType) {
+    switch ((virDomainVirtType)def->virtType) {
     case VIR_DOMAIN_VIRT_QEMU:
         virBufferAddLit(&buf, ",accel=tcg");
         break;

src/qemu/qemu_process.c

@@ -7191,6 +7191,7 @@ int qemuProcessAttach(virConnectPtr conn ATTRIBUTE_UNUSED,
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     virCapsPtr caps = NULL;
     bool active = false;
+    virDomainVirtType virtType;
 
     VIR_DEBUG("Beginning VM attach process");
 
@@ -7342,8 +7343,9 @@ int qemuProcessAttach(virConnectPtr conn ATTRIBUTE_UNUSED,
         goto exit_monitor;
     if (qemuMonitorGetStatus(priv->mon, &running, &reason) < 0)
         goto exit_monitor;
-    if (qemuMonitorGetVirtType(priv->mon, &vm->def->virtType) < 0)
+    if (qemuMonitorGetVirtType(priv->mon, &virtType) < 0)
         goto exit_monitor;
+    vm->def->virtType = virtType;
     if (qemuDomainObjExitMonitor(driver, vm) < 0)
         goto error;