Add cargo cfgs for opt in to newer standards

Currently unused, but will be needed when integrating std::optional or
std::string_view support.

    [dependencies]
    cxx = { version = "0.3", features = ["c++17"] }

1 files changed, 7 insertions, 1 deletions

diff --git a/build.rs b/build.rs
index 9a071fe5..a412dbda 100644
--- a/build.rs
+++ b/build.rs
@@ -3,7 +3,13 @@ fn main() {
         .file("src/cxx.cc")
         .cpp(true)
         .cpp_link_stdlib(None) // linked via link-cplusplus crate
-        .flag_if_supported("-std=c++11")
+        .flag_if_supported(if cfg!(feature = "c++17") {
+            "-std=c++17"
+        } else if cfg!(feature = "c++14") {
+            "-std=c++14"
+        } else {
+            "-std=c++11"
+        })
         .compile("cxxbridge03");
     println!("cargo:rerun-if-changed=src/cxx.cc");
     println!("cargo:rerun-if-changed=include/cxx.h");