[gn build] Fix link with ld.bfd and gold.

[deepinthebuild]

Summary

lld's symbol resolution algorithm makes it not depend on
the order of object files and libraries, but ld.bfd and
gold require listing dependencies later on the link line.
Put {{libs}} after {{inputs}} so that e.g. -lpthreads
appears after the object files, not before it.

https://reviews.llvm.org/differential/diff/267997/

[thakis]

lgtm, thanks!

llvm/utils/gn/build/toolchain/BUILD.gn

tool("alink") {
       outputs = [ "{{output_dir}}/{{target_output_name}}.a" ]
       output_prefix = "lib"
       default_output_dir = "{{root_out_dir}}/lib"
     }
 
     tool("solink") {
       outfile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
       if (current_os == "mac") {
-        command = "$ld -shared {{ldflags}} -o $outfile {{libs}} {{inputs}}"
+        command = "$ld -shared {{ldflags}} -o $outfile {{inputs}} {{libs}}"
         default_output_extension = ".dylib"
       } else {
-        command = "$ld -shared {{ldflags}} -Wl,-z,defs -Wl,-soname,{{target_output_name}}{{output_extension}} -o $outfile {{libs}} {{inputs}}"
+        command = "$ld -shared {{ldflags}} -Wl,-z,defs -Wl,-soname,{{target_output_name}}{{output_extension}} -o $outfile {{inputs}} {{libs}}"
         default_output_extension = ".so"
       }
       description = "SOLINK $outfile"
       outputs = [ outfile ]
       lib_switch = "-l"
       output_prefix = "lib"
       default_output_dir = "{{root_out_dir}}/lib"
     }
 
     tool("solink_module") {
       outfile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
       if (current_os == "mac") {
-        command = "$ld -shared {{ldflags}} -Wl,-flat_namespace -Wl,-undefined,suppress -o $outfile {{libs}} {{inputs}}"
+        command = "$ld -shared {{ldflags}} -Wl,-flat_namespace -Wl,-undefined,suppress -o $outfile {{inputs}} {{libs}}"
         default_output_extension = ".dylib"
       } else {
-        command = "$ld -shared {{ldflags}} -Wl,-soname,{{target_output_name}}{{output_extension}} -o $outfile {{libs}} {{inputs}}"
+        command = "$ld -shared {{ldflags}} -Wl,-soname,{{target_output_name}}{{output_extension}} -o $outfile {{inputs}} {{libs}}"
         default_output_extension = ".so"
       }
       description = "SOLINK $outfile"
       outputs = [ outfile ]
       lib_switch = "-l"
       default_output_dir = "{{root_out_dir}}/lib"
     }
 
     tool("link") {
       outfile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
       if (current_os == "mac") {
-        command = "$ld {{ldflags}} -o $outfile {{libs}} {{inputs}}"
+        command = "$ld {{ldflags}} -o $outfile {{inputs}} {{libs}}"
       } else {
-        command = "$ld {{ldflags}} -o $outfile {{libs}} -Wl,--start-group {{inputs}} -Wl,--end-group"
+        command = "$ld {{ldflags}} -o $outfile -Wl,--start-group {{inputs}} -Wl,--end-group {{libs}}"
       }
       description = "LINK $outfile"
       outputs = [ outfile ]
       lib_switch = "-l"
 
       # Setting this allows targets to override the default executable output by
       # setting output_dir.
       default_output_dir = "{{root_out_dir}}/bin"
tool("alink") {
     default_output_dir = "{{root_out_dir}}/lib"
   }
 
   tool("solink") {
     outprefix = "{{output_dir}}/{{target_output_name}}"
     dllfile = "$outprefix{{output_extension}}"
     libfile = "$outprefix.lib"
     pdbfile = "$outprefix.pdb"
-    command = "$link /nologo /dll {{ldflags}} /out:$dllfile /implib:$libfile /pdb:$pdbfile {{libs}} {{inputs}}"
+    command = "$link /nologo /dll {{ldflags}} /out:$dllfile /implib:$libfile /pdb:$pdbfile {{inputs}} {{libs}} "
     description = "LINK $dllfile"
     link_output = libfile
     depend_output = libfile
     runtime_outputs = [ dllfile ]
     outputs = [
       dllfile,
       libfile,
     ]
toolchain("win") {
   # Plugins for opt and clang and so on don't work in LLVM's Windows build
   # since the code doesn't have export annotations, but there are a few
   # standalone loadable modules used for unit-testing LLVM's dynamic library
   # loading code.
   tool("solink_module") {
     outprefix = "{{output_dir}}/{{target_output_name}}"
     dllfile = "$outprefix{{output_extension}}"
     pdbfile = "$outprefix.pdb"
-    command = "$link /nologo /dll {{ldflags}} /out:$dllfile /pdb:$pdbfile {{libs}} {{inputs}}"
+    command = "$link /nologo /dll {{ldflags}} /out:$dllfile /pdb:$pdbfile {{inputs}} {{libs}} "
     description = "LINK_MODULE $dllfile"
     outputs = [ dllfile ]
     lib_switch = ""
     runtime_outputs = outputs
     default_output_extension = ".dll"
 
     # No default_output_dir, all clients set output_dir.
   }
 
   tool("link") {
     outprefix = "{{output_dir}}/{{target_output_name}}"
     outfile = "$outprefix{{output_extension}}"
     pdbfile = "$outprefix.pdb"
-    command = "$link /nologo {{ldflags}} /out:$outfile /pdb:$pdbfile {{libs}} {{inputs}}"
+    command = "$link /nologo {{ldflags}} /out:$outfile /pdb:$pdbfile {{inputs}} {{libs}}"
     description = "LINK $outfile"
     outputs = [ outfile ]
     lib_switch = ""
     default_output_extension = ".exe"
 
     # Setting this allows targets to override the default executable output by
     # setting output_dir.
     default_output_dir = "{{root_out_dir}}/bin"