build.rs: Don't try to set linker flags since we're not linking.

First, we were passing `-Wl,--gc-sections` to the compiler regardless
of whether it is MSVC, which didn't make any sense on its own.

But, even more generally, it doesn't make sense for us to try to tell
the linker what to do when we aren't actually linking. (We're building
static libraries of the C and assembly code.)

build.rs

@@ -509,14 +509,6 @@ fn build_library(
     // Rebuild the library if necessary.
     let lib_path = PathBuf::from(out_dir).join(format!("lib{}.a", lib_name));
 
-    match target.os.as_str() {
-        "macos" => {
-            let _ = c.flag("-Wl,-dead_strip");
-        }
-        _ => {
-            let _ = c.flag("-Wl,--gc-sections");
-        }
-    }
     for o in objs {
         let _ = c.object(o);
     }