Report meaningful error if parsing a version pragma failed

test/libsolidity/SemVerMatcher.cpp

@@ -58,11 +58,12 @@ SemVerMatchExpression parseExpression(string const& _input)
 	}
 
 	auto expression = SemVerMatchExpressionParser(tokens, literals).parse();
+	BOOST_REQUIRE(expression.has_value());
 	BOOST_CHECK_MESSAGE(
-		expression.isValid(),
+		expression->isValid(),
 		"Expression \"" + _input + "\" did not parse properly."
 	);
-	return expression;
+	return *expression;
 }
 
 }

test/libsolidity/syntaxTests/pragma/broken_version_1.sol

@@ -0,0 +1,3 @@
+pragma solidity ^0^1;
+// ----
+// ParserError 5333: (0-21): Source file requires different compiler version (current compiler is ....

test/libsolidity/syntaxTests/pragma/broken_version_2.sol

@@ -0,0 +1,3 @@
+pragma solidity pragma;
+// ----
+// ParserError 1684: (0-23): Found version pragma, but failed to parse it. Please ensure there is a trailing semicolon.

test/libsolidity/syntaxTests/pragma/broken_version_3.sol

@@ -0,0 +1,4 @@
+pragma solidity #8.0.0;
+// ----
+// ParserError 6281: (16-17): Token incompatible with Solidity parser as part of pragma directive.
+// ParserError 5333: (0-23): Source file requires different compiler version (current compiler is ....

test/libsolidity/syntaxTests/pragma/broken_version_4.sol

@@ -0,0 +1,3 @@
+pragma solidity (8.0.0);
+// ----
+// ParserError 1684: (0-24): Found version pragma, but failed to parse it. Please ensure there is a trailing semicolon.

test/libsolidity/syntaxTests/pragma/broken_version_5.sol

@@ -0,0 +1,3 @@
+pragma solidity 88_;
+// ----
+// ParserError 1684: (0-20): Found version pragma, but failed to parse it. Please ensure there is a trailing semicolon.

test/libsolidity/syntaxTests/pragma/unterminated_pragma.sol

@@ -0,0 +1,3 @@
+pragma solidity 0.4.3
+// ----
+// ParserError 2314: (22-22): Expected ';' but got end of source

test/libsolidity/syntaxTests/pragma/unterminated_version.sol

@@ -0,0 +1,4 @@
+pragma solidity 0.4.3
+pragma abicoder v2;
+// ----
+// ParserError 1684: (0-41): Found version pragma, but failed to parse it. Please ensure there is a trailing semicolon.