Move logic for resolving function call overloads.

This code previously lived in FunctionCallExpr but is now part
of FunctionSymbolExpr.  This change doesn't change any current
functionality, but lays groundwork for function pointers in
the language, where we'll want to do function call overload
resolution at other times besides when a function call is
actually being made.

expr.h

@@ -42,8 +42,6 @@
 #include "ast.h"
 #include "type.h"
 
-class FunctionSymbolExpr;
-
 /** @brief Expr is the abstract base class that defines the interface that
     all expression types must implement.
  */
@@ -266,10 +264,6 @@ public:
     ExprList *args;
     bool isLaunch;
     Expr *launchCountExpr;
-
-private:
-    void resolveFunctionOverloads(bool exactMatchOnly);
-    bool tryResolve(int (*matchFunc)(Expr *, const Type *));
 };
 
 
@@ -495,7 +489,8 @@ private:
     probably-different type. */
 class TypeCastExpr : public Expr {
 public:
-    TypeCastExpr(const Type *t, Expr *e, SourcePos p);
+    TypeCastExpr(const Type *t, Expr *e, bool preserveUniformity,
+                 SourcePos p);
 
     llvm::Value *GetValue(FunctionEmitContext *ctx) const;
     const Type *GetType() const;
@@ -506,6 +501,7 @@ public:
 
     const Type *type;
     Expr *expr;
+    bool preserveUniformity;
 };
 
 
@@ -581,8 +577,12 @@ public:
     void Print() const;
     int EstimateCost() const;
 
+    bool ResolveOverloads(const std::vector<Expr *> &args);
+    Symbol *GetMatchingFunction();
+
 private:
-    friend class FunctionCallExpr;
+    bool tryResolve(int (*matchFunc)(Expr *, const Type *),
+                    const std::vector<Expr *> &args);
 
     /** Name of the function that is being called. */
     std::string name;
@@ -592,8 +592,7 @@ private:
         overload is the best match. */
     std::vector<Symbol *> *candidateFunctions;
 
-    /** The actual matching function found after overload resolution; this
-        value is set by FunctionCallExpr::resolveFunctionOverloads() */
+    /** The actual matching function found after overload resolution. */
     Symbol *matchingFunc;
 };