maint: add syntax check to prohibit static zero init

Now that all offenders have been cleaned, turn on a syntax-check
rule to prevent future offenders.

* cfg.mk (sc_prohibit_static_zero_init): New rule.
* src/qemu/qemu_driver.c (qemuDomainBlockJobImpl): Avoid false
positive.
Signed-off-by: NEric Blake <eblake@redhat.com>

cfg.mk

@@ -962,6 +962,14 @@ sc_prohibit_paren_brace:
 	halt='Put space between closing parenthesis and opening brace'	\
 	  $(_sc_search_regexp)
 
+# C guarantees that static variables are zero initialized, and some compilers
+# waste space by sticking explicit initializers in .data instead of .bss
+sc_prohibit_static_zero_init:
+	@prohibit='\bstatic\b.*= *(0[^xX0-9]|NULL|false)'		\
+	in_vc_files='\.[chx](\.in)?$$'					\
+	halt='static variables do not need explicit zero initialization'\
+	  $(_sc_search_regexp)
+
 # FreeBSD exports the "devname" symbol which produces a warning.
 sc_prohibit_devname:
 	@prohibit='\bdevname\b'	\

src/qemu/qemu_driver.c

@@ -15671,8 +15671,9 @@ qemuDomainBlockJobImpl(virDomainObjPtr vm,
              * that back into the return status of this API call.  */
             while (1) {
                 /* Poll every 50ms */
-                static struct timespec ts = { .tv_sec = 0,
-                                              .tv_nsec = 50 * 1000 * 1000ull };
+                static struct timespec ts = {
+                    .tv_sec = 0,
+                    .tv_nsec = 50 * 1000 * 1000ull };
                 virDomainBlockJobInfo dummy;
 
                 qemuDomainObjEnterMonitor(driver, vm);