Add a test for Static Analyzer checker plugins

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198820 91177308-0d34-0410-b5e6-96231b3b80d8

test/Analysis/checker-plugins.c

+// RUN: %clang_cc1 -load %llvmshlibdir/SampleAnalyzerPlugin%pluginext -analyze -analyzer-checker='example.MainCallChecker' -verify %s
+// REQUIRES: plugins, examples
+
+// Test that the MainCallChecker example analyzer plugin loads and runs.
+
+int main();
+
+void caller() {
+  main(); // expected-warning {{call to main}}
+}