[lld][WebAssembly] Do not remove name section with --strip-debug

[dschuff]

Summary

Leave the name section in the output when using the --strip-debug
flag. This treats it more like ELF symbol tables, as the name
section has similar uses at runtime (e.g. wasm engines understand
it and it can be used for symbolization at runtime).

Fixes https://github.com/emscripten-core/emscripten/issues/14623

lld/test/wasm/strip-debug.test

 RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %p/Inputs/start.s -o %t.start.o
 RUN: wasm-ld --strip-debug -o %t.wasm %t.start.o
 RUN: obj2yaml %t.wasm | FileCheck %s
 
 # Test alias -S
 RUN: wasm-ld -S -o %t.wasm %t.start.o
 RUN: obj2yaml %t.wasm | FileCheck %s
 
-# Check that there is no name section
-CHECK-NOT:   Name:    name
+# Check that there is a name section
+CHECK:   Name:    name

lld/test/wasm/weak-undefined.s

 # RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
-# RUN: wasm-ld -strip-debug %t.o -o %t.wasm
+# RUN: wasm-ld -strip-all %t.o -o %t.wasm
 # RUN: obj2yaml %t.wasm | FileCheck %s
 
 # Test that undefined weak externals (global_var) and (foo) don't cause
 # link failures and resolve to zero.
 
 .functype foo () -> (i32)
 
 .globl  get_address_of_foo

lld/wasm/SyntheticSections.h

 };
 
 // Create the custom "name" section containing debug symbol names.
 class NameSection : public SyntheticSection {
 public:
   NameSection(ArrayRef<OutputSegment *> segments)
       : SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, "name"),
         segments(segments) {}
-  bool isNeeded() const override {
-    return !config->stripDebug && !config->stripAll && numNames() > 0;
-  }
+  bool isNeeded() const override { return !config->stripAll && numNames() > 0; }
   void writeBody() override;
   unsigned numNames() const { return numNamedGlobals() + numNamedFunctions(); }
   unsigned numNamedGlobals() const;
   unsigned numNamedFunctions() const;
   unsigned numNamedDataSegments() const;
 
 protected:
   ArrayRef<OutputSegment *> segments;