Fix /domain/features setting in qemuParseCommandLine

Commit 5e6ce1 moved down detection of the ACPI feature in
qemuParseCommandLine. However, when ACPI is detected, it clears
all feature flags in def->features to only set ACPI. This used to
be fine because this was the first place were def->features was set,
but after the move this is no longer necessarily true because this
block comes before the ACPI check:

if (strstr(def->emulator, "kvm")) {
    def->virtType = VIR_DOMAIN_VIRT_KVM;
    def->features |= (1 << VIR_DOMAIN_FEATURE_PAE);
}

Since def is allocated in qemuParseCommandLine using VIR_ALLOC, we
can always use |= when modifying def->features
(cherry picked from commit 626dd5180e)

src/qemu/qemu_command.c

@@ -7435,7 +7435,7 @@ virDomainDefPtr qemuParseCommandLine(virCapsPtr caps,
         goto no_memory;
 
     if (STREQ(def->os.arch, "i686")||STREQ(def->os.arch, "x86_64"))
-        def->features = (1 << VIR_DOMAIN_FEATURE_ACPI)
+        def->features |= (1 << VIR_DOMAIN_FEATURE_ACPI)
         /*| (1 << VIR_DOMAIN_FEATURE_APIC)*/;
 #define WANT_VALUE()                                                   \
     const char *val = progargv[++i];                                   \

tests/qemuxml2argvdata/qemuxml2argv-kvmclock.xml

@@ -8,6 +8,9 @@
     <type arch='i686' machine='pc'>hvm</type>
     <boot dev='network'/>
   </os>
+  <features>
+    <pae/>
+  </features>
   <clock offset='utc'>
     <timer name='kvmclock' present='no'/>
   </clock>