Warns if modifier uses msg.value in non-payable function.

test/libsolidity/syntaxTests/viewPureChecker/msg_value_modifier.sol

@@ -0,0 +1,6 @@
+contract C {
+    modifier m(uint _amount, uint _avail) { require(_avail >= _amount); _; }
+    function f() m(1 ether, msg.value) public pure {}
+}
+// ----
+// TypeError: (118-127): Function declared as pure, but this expression (potentially) reads from the environment or state and thus requires "view".

test/libsolidity/syntaxTests/viewPureChecker/msg_value_modifier_view.sol

@@ -0,0 +1,6 @@
+contract C {
+    modifier m(uint _amount, uint _avail) { require(_avail >= _amount); _; }
+    function f() m(1 ether, msg.value) public view {}
+}
+// ----
+// Warning: (118-127): "msg.value" used in non-payable function. Do you want to add the "payable" modifier to this function?