Add tiny C example of null pointer error.

infer/src/llvm/examples/null_deref.c

@@ -0,0 +1,4 @@
+void foo(void) {
+   int *p = 0;
+   *p = 42;
+}

infer/src/llvm/examples/null_deref.ll

@@ -0,0 +1,18 @@
+; ModuleID = 'null_deref.c'
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.10.0"
+
+; Function Attrs: nounwind ssp uwtable
+define void @foo() #0 {
+  %p = alloca i32*, align 8
+  store i32* null, i32** %p, align 8
+  %1 = load i32** %p, align 8
+  store i32 42, i32* %1, align 4
+  ret void
+}
+
+attributes #0 = { nounwind ssp uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.ident = !{!0}
+
+!0 = metadata !{metadata !"Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)"}