Auto merge of #117962 - weihanglo:debug-name-table, r=wesleywiser

fix: stop emitting `.debug_pubnames` and `.debug_pubtypes`

A continuation of #94181.
Fixes #48762
MCP can be found in <https://github.com/rust-lang/compiler-team/issues/688>.

`.debug_pubnames` and `.debug_pubtypes` are poorly designed and people
seldom use them. However, they take a considerable portion of size in
the final binary. This tells LLVM stop emitting those sections on
DWARFv4 or lower. DWARFv5 use `.debug_names` which is more concise
in size and performant for name lookup.

Some other no-really-useful personal notes:

<details><summary>Details</summary>
<p>

## Pepole saying they are not useful

* https://github.com/rust-lang/rust/issues/48762
* https://rust-lang.zulipchat.com/#narrow/stream/317568-t-compiler.2Fwg-debugging/topic/investigating.20debuginfo.20size/near/342713604
* `DwarfCompileUnit::hasDwarfPubSections()` — f633f325a1/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp (L1477-L1494)
* clang default to no debug name table when no option provided — f633f325a1/clang/lib/Frontend/CompilerInvocation.cpp (L1819-L1824)
* GCC explicitly says GDB doesn't use pub sections (`TARGET_WANT_DEBUG_PUB_SECTIONS` only be true on Darwin) — 5d2a360f0a/gcc/target.def (L6985-L6990) and 319b460545/gold/dwarf_reader.h (L424-L427)
* Probably the only place that makes use of pub section in lldb — 725115d7bb/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp (L2117-L2135)

* "The -gsplit-dwarf option requires -ggnu-pubnames." — 5d2a360f0a/gcc/opts.cc (L1205)

* LLVM: Always emit `.debug_names` with dwarf 5 for Apple platforms — https://reviews.llvm.org/D118754

</p>
</details>

tests/assembly/dwarf4.rs

@@ -0,0 +1,24 @@
+// Makes sure that `-Z dwarf-version=4` causes `rustc` to emit DWARF version 4.
+// assembly-output: emit-asm
+// compile-flags: -g --target x86_64-unknown-linux-gnu -Z dwarf-version=4 -Copt-level=0
+// needs-llvm-components: x86
+
+#![feature(no_core, lang_items)]
+#![crate_type = "rlib"]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+#[lang = "copy"]
+trait Copy {}
+
+pub fn wibble() {}
+
+pub struct X;
+
+// CHECK: .section .debug_info
+// CHECK-NOT: .short 2
+// CHECK-NOT: .short 5
+// CHECK: .short 4
+// CHECK-NOT: .section .debug_pubnames
+// CHECK-NOT: .section .debug_pubtypes

tests/assembly/dwarf5.rs

@@ -18,3 +18,4 @@ pub fn wibble() {}
 // CHECK-NOT: .short 2
 // CHECK-NOT: .short 4
 // CHECK: .short 5
+// CHECK: .section .debug_names