C++: add calling convention specifier class

Author: IdrissRio

cpp/ql/lib/semmle/code/cpp/Specifier.qll

@@ -97,6 +97,16 @@ class AccessSpecifier extends Specifier {
   override string getAPrimaryQlClass() { result = "AccessSpecifier" }
 }
 
+/**
+ * A C/C++ calling convention specifier: `cdecl`, `fastcall`, `stdcall`, `thiscall`,
+ * `vectorcall`, or `clrcall`.
+ */
+class CallingConventionSpecifier extends Specifier {
+  CallingConventionSpecifier() { this.hasName(["cdecl", "fastcall", "stdcall", "thiscall", "vectorcall", "clrcall"]) }
+
+  override string getAPrimaryQlClass() { result = "CallingConventionSpecifier" }
+}
+
 /**
  * An attribute introduced by GNU's `__attribute__((name))` syntax,
  * Microsoft's `__declspec(name)` syntax, Microsoft's `[name]` syntax, the