[analyzer] Trust _Nonnull annotations for system framework

Changes the analyzer to believe that methods annotated with _Nonnull
from system frameworks indeed return non null objects.
Local methods with such annotation are still distrusted.
rdar://24291919

Differential Revision: https://reviews.llvm.org/D44341

llvm-svn: 328282
diff --git a/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt b/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt
index baf36e0..d472ae4 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt
+++ b/clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt
@@ -84,6 +84,7 @@
   TaintTesterChecker.cpp
   TestAfterDivZeroChecker.cpp
   TraversalChecker.cpp
+  TrustNonnullChecker.cpp
   UndefBranchChecker.cpp
   UndefCapturedBlockVarChecker.cpp
   UndefResultChecker.cpp