[C API] Prevent nullptr dereferences in C API for counting attributes.

See https://reviews.llvm.org/D26392

Patch by @maleadt

llvm-svn: 287044
diff --git a/llvm/tools/llvm-c-test/main.c b/llvm/tools/llvm-c-test/main.c
index 90d3501..9bc0c96 100644
--- a/llvm/tools/llvm-c-test/main.c
+++ b/llvm/tools/llvm-c-test/main.c
@@ -88,6 +88,10 @@
     return llvm_add_named_metadata_operand();
   } else if (argc == 2 && !strcmp(argv[1], "--set-metadata")) {
     return llvm_set_metadata();
+  } else if (argc == 2 && !strcmp(argv[1], "--test-function-attributes")) {
+    return llvm_test_function_attributes();
+  } else if (argc == 2 && !strcmp(argv[1], "--test-callsite-attributes")) {
+    return llvm_test_callsite_attributes();
   } else if (argc == 2 && !strcmp(argv[1], "--echo")) {
     return llvm_echo();
   } else if (argc == 2 && !strcmp(argv[1], "--test-diagnostic-handler")) {