Update llvm-nm -s to use a multi-var option

[mtrent]

Summary

Previously llvm-nm relied on a positional parameter to read two values
into the SegSect list. This worked, but required the "-s" paramater and
its arguments to be the last elements on the command-line.

The CommandLine library now supports mutli-var parameters, so it can
naturally deal with "-s" expecting two arguments, and now the input file
can appear anywhere (within reason) in the command line invocation. E.g.

llvm-nm -s __TEXT __text /bin/ls
llvm-nm /bin/ls -s __TEXT __text

rdar://27284011

[pete]

Looks good. That’s nice to see more lines removed than added :)

[MaskRay]

It seems that we have some parsing difficulty here:/ I tried to use llvm-nm -s today for --print-armap (GNU/FreeBSD nm) and I noticed that -s is reserved for Mach-O. https://www.unix.com/man-page/osx/1/nm/ says

-s segname sectname
List only those symbols in the section (segname,sectname).

This also appears to be the last use case of cl::multi_val:/ Does -s have a longer option for the SegSect functionality? After all, it has been broken so many years... (the only order which was supported was llvm-nm /bin/ls -s __TEXT __text before this patch).

[mtrent]

In D62070#2000628, @MaskRay wrote:

It seems that we have some parsing difficulty here:/ I tried to use llvm-nm -s today for --print-armap (GNU/FreeBSD nm) and I noticed that -s is reserved for Mach-O. https://www.unix.com/man-page/osx/1/nm/ says

-s segname sectname
List only those symbols in the section (segname,sectname).

This also appears to be the last use case of cl::multi_val:/ Does -s have a longer option for the SegSect functionality? After all, it has been broken so many years... (the only order which was supported was llvm-nm /bin/ls -s __TEXT __text before this patch).

There is no long form replacement for -s.

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

cl::opt<bool> JustSymbolName("just-symbol-name",
                              cl::desc("Print just the symbol's name"),
                              cl::cat(NMCat));
 cl::alias JustSymbolNames("j", cl::desc("Alias for --just-symbol-name"),
                           cl::aliasopt(JustSymbolName), cl::Grouping);
 
 cl::opt<bool> SpecialSyms("special-syms",
                           cl::desc("No-op. Used for GNU compatibility only"));
 
-// FIXME: This option takes exactly two strings and should be allowed anywhere
-// on the command line.  Such that "llvm-nm -s __TEXT __text foo.o" would work.
-// But that does not as the CommandLine Library does not have a way to make
-// this work.  For now the "-s __TEXT __text" has to be last on the command
-// line.
-cl::list<std::string> SegSect("s", cl::Positional, cl::ZeroOrMore,
+cl::list<std::string> SegSect("s", cl::multi_val(2), cl::ZeroOrMore,
                               cl::value_desc("segment section"), cl::Hidden,
                               cl::desc("Dump only symbols from this segment "
                                        "and section name, Mach-O only"),
                               cl::cat(NMCat));
 
 cl::opt<bool> FormatMachOasHex("x",
                                cl::desc("Print symbol entry in hex, "
                                         "Mach-O only"),