open your c_cpp_properties file in the project, add as follow configurations.i use of the clang.
"c-cpp-flylint.clang.includePaths": [
"${workspaceRoot}",
".",
"C:/llvm/lib/gcc/x86_64-w64-mingw32/7.1.0/include/c++",
"C:/llvm/lib/gcc/x86_64-w64-mingw32/7.1.0/include/c++/x86_64-w64-mingw32",
"C:/llvm/lib/gcc/x86_64-w64-mingw32/7.1.0/include/c++/backward",
"C:/llvm/lib/gcc/x86_64-w64-mingw32/7.1.0/include",
"C:/llvm/include",
"C:/llvm/x86_64-w64-mingw32/include",
"C:/llvm/lib/gcc/x86_64-w64-mingw32/7.1.0/include-fixed",
"C:/LLVM/lib/gcc/x86_64-w64-mingw32/7.1.0/include/ssp"
]
pay attention to these path. they include necessary files when you complie,of course ,it is useful for me because of according to my files in the pc.you can custom to configure them. i hope my answer to help you out.if have any question,it is free to contect to me.