修改libc的编译相关内容(#171)

1.将libc的include文件夹分为export和internal
2.将所有app都直接链接libc.a,而不是都执行一遍"搜索.o"的过程

user/libs/libc/build.rs

@@ -0,0 +1,45 @@
+extern crate bindgen;
+// use ::std::env;
+
+use std::path::PathBuf;
+
+fn main() {
+    // Tell cargo to look for shared libraries in the specified directory
+    println!("cargo:rustc-link-search=src");
+    println!("cargo:rerun-if-changed=src/include/internal/bindings/wrapper.h");
+
+    // let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+    let out_path = PathBuf::from(String::from("src/include/internal/bindings/"));
+
+    // The bindgen::Builder is the main entry point
+    // to bindgen, and lets you build up options for
+    // the resulting bindings.
+    {
+        let bindings = bindgen::Builder::default()
+            .clang_arg("-I./src/include")
+            .clang_arg("-I./src/include/export") // todo: 当引入多种架构之后，需要修改这里，对于不同的架构编译时，include不同的路径
+            // The input header we would like to generate
+            // bindings for.
+            .header("src/include/internal/bindings/wrapper.h")
+            .clang_arg("--target=x86_64-none-none")
+            .clang_arg("-v")
+            // 使用core，并将c语言的类型改为core::ffi，而不是使用std库。
+            .use_core()
+            .ctypes_prefix("::core::ffi")
+            .generate_inline_functions(true)
+            .raw_line("#![allow(dead_code)]")
+            .raw_line("#![allow(non_upper_case_globals)]")
+            .raw_line("#![allow(non_camel_case_types)]")
+            // Tell cargo to invalidate the built crate whenever any of the
+            // included header files changed.
+            .parse_callbacks(Box::new(bindgen::CargoCallbacks))
+            // Finish the builder and generate the bindings.
+            .generate()
+            // Unwrap the Result and panic on failure.
+            .expect("Unable to generate bindings");
+
+        bindings
+            .write_to_file(out_path.join("bindings.rs"))
+            .expect("Couldn't write bindings!");
+    }
+}