gn build: Stop passing -o to ar.

[pcc]

Summary

The -o flag means something different to ar than what appears to be
intended here. Also, llvm-ar doesn't accept the flag in this position.

[phosek]

LGTM

[thakis]

Thanks for the patch! Please run git ls-files '*.gn' '*.gni' | xargs -n 1 gn format after making GN changes. (I forgot that for the PowerPC target too, so I'm running it for this file here too, so nothing to do for you, just pointing it out for next time.)

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

toolchain("unix") {
 
   tool("alink") {
     if (host_os == "mac") {
       command = "libtool -static -no_warning_for_no_symbols {{arflags}} -o {{output}} {{inputs}}"
     } else {
       # Remove the output file first so that ar doesn't try to modify the
       # existing file.
       command =
-          "rm -f {{output}} && ar rcsDT {{arflags}} -o {{output}} {{inputs}}"
+          "rm -f {{output}} && ar rcsDT {{arflags}} {{output}} {{inputs}}"
     }
     description = "AR {{output}}"
     outputs = [
       "{{output_dir}}/{{target_output_name}}.a",
     ]
     output_prefix = "lib"
     default_output_dir = "{{root_out_dir}}/lib"
   }