[Driver][DragonFly] -r: imply -nostdlib like GCC

[brad]

Summary

Similar to D116843 for Gnu.cpp

[MaskRay]

Looks great!

clang/lib/Driver/ToolChains/DragonFly.cpp

void dragonfly::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (Output.isFilename()) {
     CmdArgs.push_back("-o");
     CmdArgs.push_back(Output.getFilename());
   } else {
     assert(Output.isNothing() && "Invalid output.");
   }
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles,
+                   options::OPT_r)) {
     if (!Args.hasArg(options::OPT_shared)) {
       if (Args.hasArg(options::OPT_pg))
         CmdArgs.push_back(
             Args.MakeArgString(getToolChain().GetFilePath("gcrt1.o")));
       else {
         if (Args.hasArg(options::OPT_pie))
           CmdArgs.push_back(
               Args.MakeArgString(getToolChain().GetFilePath("Scrt1.o")));
else
           Args.MakeArgString(getToolChain().GetFilePath("crtbegin.o")));
   }
 
   Args.AddAllArgs(CmdArgs,
                   {options::OPT_L, options::OPT_T_Group, options::OPT_e});
 
   AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs, JA);
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs,
+                   options::OPT_r)) {
     CmdArgs.push_back("-L/usr/lib/gcc80");
 
     if (!Args.hasArg(options::OPT_static)) {
       CmdArgs.push_back("-rpath");
       CmdArgs.push_back("/usr/lib/gcc80");
     }
 
     if (D.CCCIsCXX()) {
if (Args.hasArg(options::OPT_static) ||
           CmdArgs.push_back("-lgcc");
           CmdArgs.push_back("--as-needed");
           CmdArgs.push_back("-lgcc_pic");
           CmdArgs.push_back("--no-as-needed");
       }
     }
   }
 
-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles,
+                   options::OPT_r)) {
     if (Args.hasArg(options::OPT_shared) || Args.hasArg(options::OPT_pie))
       CmdArgs.push_back(
           Args.MakeArgString(getToolChain().GetFilePath("crtendS.o")));
     else
       CmdArgs.push_back(
           Args.MakeArgString(getToolChain().GetFilePath("crtend.o")));
     CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath("crtn.o")));
   }

clang/test/Driver/dragonfly.c

 // RUN: %clang -no-canonical-prefixes -target x86_64-pc-dragonfly %s -### 2> %t.log
 // RUN: FileCheck -input-file %t.log %s
 
 // CHECK: clang{{.*}}" "-cc1" "-triple" "x86_64-pc-dragonfly"
 // CHECK: ld{{.*}}" "--eh-frame-hdr" "-dynamic-linker" "/usr/libexec/ld-elf.so.{{.*}}" "--hash-style=gnu" "--enable-new-dtags" "-o" "a.out" "{{.*}}crt1.o" "{{.*}}crti.o" "{{.*}}crtbegin.o" "{{.*}}.o" "-L{{.*}}gcc{{.*}}" "-rpath" "{{.*}}gcc{{.*}}" "-lc" "-lgcc" "{{.*}}crtend.o" "{{.*}}crtn.o"
 
-
+// -r suppresses default -l and crt*.o like -nostdlib.
+// RUN: %clang -### %s --target=x86_64-pc-dragonfly -r \
+// RUN:   2>&1 | FileCheck %s --check-prefix=RELOCATABLE
+// RELOCATABLE:     "-r"
+// RELOCATABLE-NOT: "-l
+// RELOCATABLE-NOT: {{.*}}crt{{[^.]+}}.o