Add an option to Builder for preprocessor defines

Cargo.lock

-[root]
-name = "cbindgen"
-version = "0.3.2"
-dependencies = [
- "clap 2.24.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.21 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_json 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
- "tempdir 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "toml 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "ansi_term"
 version = "0.9.0"
@@ -31,6 +18,19 @@ name = "bitflags"
 version = "0.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "cbindgen"
+version = "0.3.2"
+dependencies = [
+ "clap 2.24.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.21 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tempdir 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "toml 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "clap"
 version = "2.24.2"

src/bindgen/builder.rs

@@ -133,6 +133,24 @@ impl Builder {
         self
     }
 
+    #[allow(unused)]
+    pub fn with_target_os_define(mut self, platform: &str, preprocessor_define: &str) -> Builder {
+        self.config.defines.insert(
+            format!("target_os = {}", platform),
+            preprocessor_define.to_owned(),
+        );
+        self
+    }
+
+    #[allow(unused)]
+    pub fn with_define(mut self, key: &str, value: &str, preprocessor_define: &str) -> Builder {
+        self.config.defines.insert(
+            format!("{} = {}", key, value),
+            preprocessor_define.to_owned(),
+        );
+        self
+    }
+
     #[allow(unused)]
     pub fn with_config(mut self, config: Config) -> Builder {
         self.config = config;