allow installing lib and include under different prefixes

deltachat-ffi/build.rs

@@ -22,7 +22,9 @@ fn main() {
         url = env::var("CARGO_PKG_HOMEPAGE").unwrap_or_else(|_| "".to_string()),
         version = env::var("CARGO_PKG_VERSION").unwrap(),
         libs_priv = libs_priv,
-        prefix = env::var("PREFIX").unwrap_or_else(|_| "/usr/local".to_string()),
+        prefix = env::var("PREFIX").unwrap(),
+        libdir = env::var("LIBDIR").unwrap(),
+        includedir = env::var("INCLUDEDIR").unwrap(),
     );
 
     fs::create_dir_all(target_path.join("pkgconfig")).unwrap();

deltachat-ffi/deltachat.pc.in

@@ -1,6 +1,6 @@
 prefix={prefix}
-libdir=${{prefix}}/lib
-includedir=${{prefix}}/include
+libdir={libdir}
+includedir={includedir}
 
 Name: {name}
 Description: {description}