[llvm-nm] Write "no symbol" output to stderr

[phosek]

Summary

This matches the output of binutils' nm and ensures that any scripts
or tools that use nm and expect empty output in case there no symbols
don't break.

[rupprecht]

Thanks Petr, I completely missed that it was going to stderr!
There are two tests in lld and clang to update as well, see rL343743 and rL343744.

[phosek]

Thanks for pointing those out, I've included them in this change as well.

llvm/test/Object/nm-shared-object.test

 RUN: not llvm-nm -D %p/Inputs/weak-global-symbol.macho-i386 2>&1 \
 RUN:         | FileCheck %s -check-prefix ERROR
 
 RUN: not llvm-nm -D %p/Inputs/trivial-object-test.coff-i386 2>&1 \
 RUN:         | FileCheck %s -check-prefix ERROR
 
 ERROR: File format has no dynamic symbol table.
 
-RUN: llvm-nm -D %p/Inputs/trivial-object-test.elf-i386 | FileCheck %s -check-prefix=NO-SYMBOLS
+RUN: llvm-nm -D %p/Inputs/trivial-object-test.elf-i386 2>&1 \
+RUN:         | FileCheck %s -check-prefix=NO-SYMBOLS
 NO-SYMBOLS: no symbols

llvm/test/ThinLTO/X86/empty-module.ll

 ; RUN: opt -module-summary -o %t.bc %s
 
 ; RUN: rm -f %t2.0
 ; RUN: llvm-lto2 run  %t.bc -r %t.bc,foo,pl -o %t2 -thinlto-distributed-indexes
 ; RUN: llvm-readobj -h %t2.0 | FileCheck %s
-; RUN: llvm-nm %t2.0 | FileCheck %s -check-prefix=NO-SYMBOLS
+; RUN: llvm-nm %t2.0 2>&1 | FileCheck %s -check-prefix=NO-SYMBOLS
 ; NO-SYMBOLS: no symbols
 
 ; CHECK: Format: ELF64-x86-64
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @foo = ifunc i32 (i32), i64 ()* @foo_ifunc
 
 define internal i64 @foo_ifunc() {
 entry:
   ret i64 0
 }

llvm/test/tools/llvm-nm/X86/nm-no-symbols.test

 # RUN: yaml2obj %s > %t.o
-# RUN: llvm-nm %t.o | FileCheck %s
-# RUN: llvm-nm --print-file-name %t.o | FileCheck %s --check-prefix=CHECK-PRINT-FILE-NAME
+# RUN: llvm-nm %t.o 2>&1 | FileCheck %s
+# RUN: llvm-nm --print-file-name %t.o 2>&1 | FileCheck %s --check-prefix=CHECK-PRINT-FILE-NAME
 
 !ELF
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
   Type:            ET_REL
   Machine:         EM_X86_64
 
 # CHECK: {{^}}no symbols{{$}}
 
 # CHECK-PRINT-FILE-NAME: nm-no-symbols.test{{.*}}.o: no symbols{{$}}

llvm/tools/llvm-nm/llvm-nm.cpp

if (isSymbolList64Bit(Obj)) {
     case Radix::x:
       printFormat = OutputFormat == posix ? "%" PRIx64 : "%08" PRIx64;
       break;
     default:
       printFormat = OutputFormat == posix ? "%" PRId64 : "%08" PRId64;
     }
   }
 
-  auto writeFileName = [&]() {
+  auto writeFileName = [&](raw_ostream &S) {
     if (!ArchitectureName.empty())
-      outs() << "(for architecture " << ArchitectureName << "):";
+      S << "(for architecture " << ArchitectureName << "):";
     if (OutputFormat == posix && !ArchiveName.empty())
-      outs() << ArchiveName << "[" << CurrentFilename << "]: ";
+      S << ArchiveName << "[" << CurrentFilename << "]: ";
     else {
       if (!ArchiveName.empty())
-        outs() << ArchiveName << ":";
-      outs() << CurrentFilename << ": ";
+        S << ArchiveName << ":";
+      S << CurrentFilename << ": ";
     }
   };
 
   if (SymbolList.empty()) {
     if (PrintFileName)
-      writeFileName();
-    outs() << "no symbols\n";
+      writeFileName(errs());
+    errs() << "no symbols\n";
   }
 
   for (SymbolListT::iterator I = SymbolList.begin(), E = SymbolList.end();
        I != E; ++I) {
     uint32_t SymFlags;
     std::string Name = I->Name.str();
     MachOObjectFile *MachO = dyn_cast<MachOObjectFile>(&Obj);
     if (Demangle) {
       if (Optional<std::string> Opt = demangle(I->Name, MachO))
         Name = *Opt;
     }
     if (I->Sym.getRawDataRefImpl().p)
       SymFlags = I->Sym.getFlags();
     else
       SymFlags = I->SymFlags;
 
     bool Undefined = SymFlags & SymbolRef::SF_Undefined;
     bool Global = SymFlags & SymbolRef::SF_Global;
     bool Weak = SymFlags & SymbolRef::SF_Weak;
     if ((!Undefined && UndefinedOnly) || (Undefined && DefinedOnly) ||
         (!Global && ExternalOnly) || (SizeSort && !PrintAddress) ||
         (Weak && NoWeakSymbols))
       continue;
     if (PrintFileName)
-      writeFileName();
+      writeFileName(outs());
     if ((JustSymbolName ||
          (UndefinedOnly && MachO && OutputFormat != darwin)) &&
         OutputFormat != posix) {
       outs() << Name << "\n";
       continue;
     }
 
     char SymbolAddrStr[18] = "";