[clang][hexagon] Handle library path arguments earlier

[bcain]

Summary

The removal of the early return in 96832a6bf7e0e7f1e8d634d38c44a1b32d512923
was an error: it would include the 'standalone' library that's not used
by linux.

Instead we reproduce the library path handling in the linux/musl block.

[MaskRay]

(After D156363, newer tests can use -### -Werror instead of -fdriver-only -v -Werror :) )

[bcain]

Changed test to use -Werror -### instead of -fdriver-only -v -Werror.

Fixed indentation / clang-format.

[bcain]

ping? any concerns about this change?

[sidneym]

LGTM

clang/lib/Driver/ToolChains/Hexagon.cpp

if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
 
       CmdArgs.push_back("-lclang_rt.builtins-hexagon");
       CmdArgs.push_back("-lc");
     }
     if (D.CCCIsCXX()) {
       if (HTC.ShouldLinkCXXStdlib(Args))
         HTC.AddCXXStdlibLibArgs(Args, CmdArgs);
     }
+    const ToolChain::path_list &LibPaths = HTC.getFilePaths();
+    for (const auto &LibPath : LibPaths)
+      CmdArgs.push_back(Args.MakeArgString(StringRef("-L") + LibPath));
+    Args.ClaimAllArgs(options::OPT_L);
+    return;
   }
 
   //----------------------------------------------------------------------------
   // moslib
   //----------------------------------------------------------------------------
   std::vector<std::string> OsLibs;
   bool HasStandalone = false;
   for (const Arg *A : Args.filtered(options::OPT_moslib_EQ)) {

clang/test/Driver/hexagon-toolchain-linux.c

 // RUN:   -resource-dir=%S/Inputs/resource_dir \
 // RUN:   %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK009 %s
 // CHECK009:   InstalledDir: [[INSTALLED_DIR:.+]]
 // CHECK009:   "-resource-dir" "[[RESOURCE:[^"]+]]"
 // CHECK009-SAME: {{^}} "-internal-isystem" "[[RESOURCE]]/include"
 // CHECK009-SAME: {{^}} "-internal-externc-isystem" "[[INSTALLED_DIR]]/../target/hexagon/include"
 
-// RUN: %clang -fdriver-only -Werror -v -L/tmp \
-// RUN:    --target=hexagon-unknown-linux-musl %s 2>&1 \
+// RUN: %clang -Werror -L/tmp \
+// RUN:    --target=hexagon-unknown-linux-musl %s -### 2>&1 \
 // RUN:    | FileCheck -check-prefix=CHECK010 %s
 // CHECK010:   InstalledDir: [[INSTALLED_DIR:.+]]
+// CHECK010-NOT:  "-lstandalone"
+// CHECK010-NOT:  crt0_standalone.o
+// CHECK010:   crt1.o
 // CHECK010:   "-L/tmp"
+// CHECK010-NOT:  "-lstandalone"