[Driver] Delete redundant -Bdynamic for libc++ on Fuchsia

[MaskRay]

Summary

The surrounding --push-state saves the "-Bdynamic" state across ld.bfd, gold and lld.
lld saves the least states, but the intersection of these linkers is --as-needed -Bdynamic --whole-archive

ld/ldlang.h: lang_input_statement_flags::dynamic
gold/options.h: Position_dependent_options::copy_from_options
lld/ELF/Driver.cpp: Stack.emplace_back(Config->AsNeeded, Config->Static, InWholeArchive);

[MaskRay]

I'm unclear if you also want as-needed -lm or if you accept static -lm

[mcgrathr]

This breaks the semantics we want. The -Bdynamic is there to apply to -lm, which is also what --as-needed is there for in this case (it appears earlier because of the conditional logic, since in the other case it applies to -lc++ as well). It's correct as is.

lib/Driver/ToolChains/Fuchsia.cpp

if (D.CCCIsCXX()) {
       if (ToolChain.ShouldLinkCXXStdlib(Args)) {
         bool OnlyLibstdcxxStatic = Args.hasArg(options::OPT_static_libstdcxx) &&
                                    !Args.hasArg(options::OPT_static);
         CmdArgs.push_back("--push-state");
         CmdArgs.push_back("--as-needed");
         if (OnlyLibstdcxxStatic)
           CmdArgs.push_back("-Bstatic");
         ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
-        if (OnlyLibstdcxxStatic)
-          CmdArgs.push_back("-Bdynamic");
         CmdArgs.push_back("-lm");
         CmdArgs.push_back("--pop-state");
       }
     }
 
     AddRunTimeLibs(ToolChain, D, CmdArgs, Args);
 
     if (Args.hasArg(options::OPT_pthread) ||

test/Driver/fuchsia.cpp

 
 // RUN: %clangxx %s -### --target=x86_64-unknown-fuchsia -static-libstdc++ \
 // RUN:     -fuse-ld=lld 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-STATIC
 // CHECK-STATIC: "--push-state"
 // CHECK-STATIC: "--as-needed"
 // CHECK-STATIC: "-Bstatic"
 // CHECK-STATIC: "-lc++"
-// CHECK-STATIC: "-Bdynamic"
 // CHECK-STATIC: "-lm"
 // CHECK-STATIC: "--pop-state"
 // CHECK-STATIC: "-lc"