writer-json-sarif: fix miscompilation with recent Apple Clang

For a reason I'm too lazy to diagnose, latest releases of Apple Clang now
ignore the outermost initializer lists with object initializers which GCC
still translates to an array.  Construct the arrays explicitly to avoid this
ambiguity.

Resolves: #160

Author: lzaoral

src/lib/writer-json-sarif.cc

@@ -362,9 +362,9 @@ void SarifTreeEncoder::appendDef(const Defect &def)
     }
 
     // codeFlows
-    result["codeFlows"] = {
+    result["codeFlows"] = array{
         // threadFlows
-        {{ "threadFlows", {
+        {{ "threadFlows", array{
             // locations
             {{ "locations", std::move(flowLocs) }}
         }}}
@@ -388,7 +388,7 @@ void SarifTreeEncoder::writeTo(std::ostream &str)
 
     if (!d->scanProps.empty()) {
         // scan props
-        root["inlineExternalProperties"] = {
+        root["inlineExternalProperties"] = array{
             {{ "externalizedProperties", jsonSerializeScanProps(d->scanProps) }}
         };
     }