Properly inform cargo that we are using some env variables

build.rs

@@ -39,6 +39,7 @@ fn ignore(path: &Path) -> bool {
 }
 
 fn find_make() -> OsString {
+    println!("cargo:rerun-if-env-changed=MAKE");
     if let Some(make) = env::var_os("MAKE") {
         make
     } else {
@@ -98,6 +99,7 @@ fn build_jsapi() {
     let target = env::var("TARGET").unwrap();
     let mut make = find_make();
     // Put MOZTOOLS_PATH at the beginning of PATH if specified
+    println!("cargo:rerun-if-env-changed=MOZTOOLS_PATH");
     if let Some(moztools) = env::var_os("MOZTOOLS_PATH") {
         let path = env::var_os("PATH").unwrap();
         let mut paths = Vec::new();
@@ -222,12 +224,14 @@ fn build_jsapi_bindings() {
         builder = builder.clang_arg("-fms-compatibility");
     }
 
+    println!("cargo:rerun-if-env-changed=CXXFLAGS");
     if let Ok(flags) = env::var("CXXFLAGS") {
         for flag in flags.split_whitespace() {
             builder = builder.clang_arg(flag);
         }
     }
 
+    println!("cargo:rerun-if-env-changed=CLANGFLAGS");
     if let Ok(flags) = env::var("CLANGFLAGS") {
         for flag in flags.split_whitespace() {
             builder = builder.clang_arg(flag);