Avoid loading the whole gdb debug scripts section.

This is so LLVM isn't forced to load every byte of it. Also sets the alignment of
the load. Adds a test for the debug script section.

src/test/codegen/function-arguments.rs

@@ -10,6 +10,7 @@
 
 // compile-flags: -C no-prepopulate-passes
 
+#![crate_type = "lib"]
 #![feature(allocator)]
 
 pub struct S {