[RISCV][Driver] Make the ordering of CmdArgs consistent between RISCV::Linker and baremetal::Linker

[arcbbb]

Summary

In baremetal::Linker::ConstructJob, LinkerInput is handled prior to T_Group options,
but on the other side in RISCV::Linker::ConstructJob, it is opposite.

We want it to be consistent whether users are using RISCV::Linker or baremetal::Linker.

[kito-cheng]

Few more word for this issue, the option order is matter for linker both for GNU ld and lld, in the test @arcbbb provided, ABC will treat as undefined in a.lds if the order is wrong.

[MaskRay]

LG.

A better test should have a few more stuff, see Xlinker-args.c
Instead of saying --defsym takes precedence over T_Group options, you can say that -T is the last.

Few more word for this issue, the option order is matter for linker both for GNU ld and lld, in the test @arcbbb provided, ABC will treat as undefined in a.lds if the order is wrong.

While GNU people may not like it, I think relying on the order between --defsym and -T is highly problematic: https://sourceware.org/pipermail/libc-alpha/2020-March/111920.html

[kito-cheng]

This comment was removed by kito-cheng.

[arcbbb]

Addressed @MaskRay 's comment

clang/lib/Driver/ToolChains/RISCVToolchain.cpp

crtend = ToolChain.getCompilerRTArgString(Args, "crtend",
                                               ToolChain::FT_Object);
   }
 
   if (WantCRTs) {
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crt0.o")));
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtbegin)));
   }
 
+  AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
+
   Args.AddAllArgs(CmdArgs, options::OPT_L);
   ToolChain.AddFilePathLibArgs(Args, CmdArgs);
   Args.AddAllArgs(CmdArgs,
                   {options::OPT_T_Group, options::OPT_e, options::OPT_s,
                    options::OPT_t, options::OPT_Z_Flag, options::OPT_r});
 
-  AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
-
   // TODO: add C++ includes and libs if compiling C++.
 
   if (!Args.hasArg(options::OPT_nostdlib) &&
       !Args.hasArg(options::OPT_nodefaultlibs)) {
     if (ToolChain.ShouldLinkCXXStdlib(Args))
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
     CmdArgs.push_back("--start-group");
     CmdArgs.push_back("-lc");

clang/test/Driver/riscv-args.c

+// Check the arguments are correctly passed
+
+// Make sure -T is the last with gcc-toolchain option
+// RUN: %clang -### -target riscv32 \
+// RUN:   --gcc-toolchain= -Xlinker --defsym=FOO=10 -T a.lds %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-LD %s
+// CHECK-LD: {{.*}} "--defsym=FOO=10" {{.*}} "-T" "a.lds"