Adding fixes for signedness warnings in libsolidity

Co-authored-by: Kamil Śliwak <kamil.sliwak@codepoets.it>

libsolidity/codegen/CompilerContext.h

@@ -377,7 +377,7 @@ private:
 	/// The runtime context if in Creation mode, this is used for generating tags that would be stored into the storage and then used at runtime.
 	CompilerContext *m_runtimeContext;
 	/// The index of the runtime subroutine.
-	size_t m_runtimeSub = -1;
+	size_t m_runtimeSub = std::numeric_limits<size_t>::max();
 	/// An index of low-level function labels by name.
 	std::map<std::string, evmasm::AssemblyItem> m_lowLevelFunctions;
 	/// Collector for yul functions.