Changed error message and added tests

test/libsolidity/syntaxTests/variableDeclaration/do_while.sol

@@ -0,0 +1,12 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		do
+			uint y;
+		while (x > 0);
+	}
+}
+// ----
+// SyntaxError: (81-87): Variable declarations can only be used inside blocks.

test/libsolidity/syntaxTests/variableDeclaration/else.sol

@@ -0,0 +1,13 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		if (x > 0)
+			{uint y;}
+		else
+			uint z;
+	}
+}
+// ----
+// SyntaxError: (109-115): Variable declarations can only be used inside blocks.

test/libsolidity/syntaxTests/variableDeclaration/for.sol

@@ -0,0 +1,11 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		for (uint i = 0; i < x; ++i)
+			uint y;
+	}
+}
+// ----
+// SyntaxError: (107-113): Variable declarations can only be used inside blocks.

test/libsolidity/syntaxTests/variableDeclaration/if.sol

@@ -0,0 +1,11 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		if (x > 0)
+			uint y;
+	}
+}
+// ----
+// SyntaxError: (89-95): Variable declarations can only be used inside blocks.

test/libsolidity/syntaxTests/variableDeclaration/while.sol

@@ -0,0 +1,11 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		while (x > 0)
+			uint y;
+	}
+}
+// ----
+// SyntaxError: (92-98): Variable declarations can only be used inside blocks.