Audit uses of apply_mark in built-in macros

Replace them with equivalents of `Span::{def_site,call_site}` from proc macro API.
The new API is much less error prone and doesn't rely on macros having default transparency.

src/libsyntax_ext/asm.rs

@@ -63,7 +63,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt<'_>,
     MacEager::expr(P(ast::Expr {
         id: ast::DUMMY_NODE_ID,
         node: ast::ExprKind::InlineAsm(P(inline_asm)),
-        span: sp.with_ctxt(cx.backtrace()),
+        span: cx.with_legacy_ctxt(sp),
         attrs: ThinVec::new(),
     }))
 }