make _rs a special static local

The _rs variable is used for printk ratelimiting, similar to __warned,
which makes it a logical candidate to be "special": don't correlate it,
yet don't mark a function as changed just because it references it.

kpatch-build/create-diff-object.c

@@ -527,6 +527,7 @@ static int is_special_static(struct symbol *sym)
 		"__warned.",
 		"descriptor.",
 		"__func__.",
+		"_rs.",
 		NULL,
 	};
 	char **prefix;

test/integration/special-static-2.patch

@@ -0,0 +1,25 @@
+Index: src/arch/x86/kvm/x86.c
+===================================================================
+--- src.orig/arch/x86/kvm/x86.c
++++ src/arch/x86/kvm/x86.c
+@@ -2011,12 +2011,20 @@ static void record_steal_time(struct kvm
+ 		&vcpu->arch.st.steal, sizeof(struct kvm_steal_time));
+ }
+ 
++void kpatch_kvm_x86_foo(void)
++{
++	if (!jiffies)
++		printk("kpatch kvm x86 foo\n");
++}
++
+ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+ {
+ 	bool pr = false;
+ 	u32 msr = msr_info->index;
+ 	u64 data = msr_info->data;
+ 
++	kpatch_kvm_x86_foo();
++
+ 	switch (msr) {
+ 	case MSR_AMD64_NB_CFG:
+ 	case MSR_IA32_UCODE_REV: