Auto merge of #143679 - sebastianpoeplau:preserve-debug-gdb-scripts-section, r=bjorn3

Preserve the .debug_gdb_scripts section

Make sure that compiler and linker don't optimize the section's contents
away by adding the global holding the data to `llvm.used`. This
eliminates the need for a volatile load in the main shim; since the LLVM
codegen backend is the only implementer of the corresponding trait
function, remove it entirely.

Pretty printers in dylib dependencies are now emitted by the main crate
instead of the dylib; apart from matching how rlibs are handled, this
approach has the advantage that `omit_gdb_pretty_printer_section` keeps
working with dylib dependencies.

r? `@bjorn3`

Author: bors

src/debuginfo.rs

@@ -254,7 +254,8 @@ impl<'gcc, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         // TODO(antoyo): implement.
     }
 
-    fn debuginfo_finalize(&self) {
+    fn debuginfo_finalize(&mut self) {
+        // TODO: emit section `.debug_gdb_scripts`.
         self.context.set_debug_info(true)
     }