C++: take IR Operand locations from definitions

Previously Operand's getLocation would take it from the Operand use.
This lead to slightly confusing query results, where for example an
issue related to a call argument would highlight the function part of
the call instead of the parameter.

cpp/ql/lib/semmle/code/cpp/ir/implementation/aliased_ssa/Operand.qll

@@ -46,7 +46,7 @@ class Operand extends TStageOperand {
   /**
    * Gets the location of the source code for this operand.
    */
-  final Language::Location getLocation() { result = this.getUse().getLocation() }
+  final Language::Location getLocation() { result = this.getAnyDef().getLocation() }
 
   /**
    * Gets the function that contains this operand.

cpp/ql/test/library-tests/ir/ir/PrintConfig.qll

@@ -1,10 +1,19 @@
 private import cpp
 
+/**
+ * Holds if an AST or IR with the specified location should be printed in the test output.
+ *
+ * This predicate excludes locations in standard headers.
+ */
+predicate shouldDump(Location loc) {
+  not loc.getFile().getAbsolutePath().regexpMatch(".*/include/[^/]+")
+}
+
 /**
  * Holds if the AST or IR for the specified function should be printed in the test output.
  *
  * This predicate excludes functions defined in standard headers.
  */
 predicate shouldDumpFunction(Function func) {
-  not func.getLocation().getFile().getAbsolutePath().regexpMatch(".*/include/[^/]+")
+  shouldDump(func.getLocation())
 }

cpp/ql/test/library-tests/ir/ir/operand_locations.ql

@@ -0,0 +1,7 @@
+private import cpp
+private import semmle.code.cpp.ir.IR
+private import PrintConfig
+
+from Operand a
+where shouldDump(a.getLocation())
+select a, a.getDumpString()