nm: Add -no-weak flag for hiding weak symbols

[keith]

Summary

This adds a new -no-weak flag to nm to hide weak symbols in its output.
This also adds a -W alias for this which is analogous to -U.

[keith]

Use count 0 instead of FileCheck for test

[keith]

Revert unnecessary FileCheck prefix

[kastiglione]

tools/llvm-nm/llvm-nm.cpp

85

This should probably be "Show only non-weak symbols" since all the rest of the descriptions are phrased affirmatively.

[keith]

Update help wording

[kastiglione]

Accepting with the following reasoning: This is consistent with the existing filtering by other symbol kinds, and is opt-in/non-breaking.

[kastiglione]

Can you also document -no-weak in docs/CommandGuide/llvm-nm.rst?

[keith]

Add --no-weak to command guide

test/tools/llvm-nm/X86/weak.test

-# RUN: llvm-nm -B -S %p/Inputs/weak.obj.elf-x86_64 | FileCheck --match-full-lines %s
+# RUN: llvm-nm -B -S %p/Inputs/weak.obj.elf-x86_64 | FileCheck --match-full-lines %s --check-prefix=WEAK
+# RUN: llvm-nm -W -B -S %p/Inputs/weak.obj.elf-x86_64 | count 0
 
-CHECK:                  w weak_extern_func
-CHECK:                  w weak_extern_var
-CHECK: 0000000000000000 0000000000000011 W weak_func
-CHECK: 0000000000000000 0000000000000004 V weak_var
+WEAK:                  w weak_extern_func
+WEAK:                  w weak_extern_var
+WEAK: 0000000000000000 0000000000000011 W weak_func
+WEAK: 0000000000000000 0000000000000004 V weak_var

tools/llvm-nm/llvm-nm.cpp

 
 cl::opt<bool> ExternalOnly("extern-only",
                            cl::desc("Show only external symbols"),
                            cl::ZeroOrMore);
 cl::alias ExternalOnly2("g", cl::desc("Alias for --extern-only"),
                         cl::aliasopt(ExternalOnly), cl::Grouping,
                         cl::ZeroOrMore);
 
+cl::opt<bool> NoWeakSymbols("no-weak",
+                            cl::desc("Don't show weak symbols"));
+cl::alias NoWeakSymbols2("W", cl::desc("Alias for --no-weak"),
+                         cl::aliasopt(NoWeakSymbols), cl::Grouping);
+
 cl::opt<bool> BSDFormat("B", cl::desc("Alias for --format=bsd"),
                         cl::Grouping);
 cl::opt<bool> POSIXFormat("P", cl::desc("Alias for --format=posix"),
                           cl::Grouping);
 cl::opt<bool> DarwinFormat("m", cl::desc("Alias for --format=darwin"),
                            cl::Grouping);
 
 static cl::list<std::string>
for (SymbolListT::iterator I = SymbolList.begin(), E = SymbolList.end();
     }
     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))
+        (!Global && ExternalOnly) || (SizeSort && !PrintAddress) ||
+        (Weak && NoWeakSymbols))
       continue;
     if (PrintFileName) {
       if (!ArchitectureName.empty())
         outs() << "(for architecture " << ArchitectureName << "):";
       if (OutputFormat == posix && !ArchiveName.empty())
         outs() << ArchiveName << "[" << CurrentFilename << "]: ";
       else {
         if (!ArchiveName.empty())