Add a target to compile every artifacts

makefile

@@ -6,6 +6,8 @@ linux-compiler = g++
 # Embed c and c++ libraries (see https://stackoverflow.com/a/6405064)
 win-compiler = i686-w64-mingw32-g++-win32 -static-libstdc++ -static-libgcc
 
+all: $(linux-artifact) $(win-artifact)
+
 $(linux-artifact): main.cpp
 	$(linux-compiler) main.cpp -o $(linux-artifact)