[BareMetal] Ensure that sysroot always comes after library paths

[phosek]

Summary

This addresses an issue introduced in D91559. We would invoke the
compiler with -Lpath/to/lib --sysroot=path/to/sysroot where both
locations contain libraries with the same name, but we expect linker
to pick up the library in path/to/lib since that version is more
specialized. This was the case before D91559 where the sysroot path
would be ignored, but after that change linker would now pick up the
library from the sysroot which resulted in unexpected behavior.

The sysroot path should always come after any user provided library
paths, followed by compiler runtime paths. We want for libraries in user
provided library paths to always take precedence over sysroot libraries.
This matches the behavior of other toolchains used with other targets.

[abidh]

LGTM

clang/lib/Driver/ToolChains/BareMetal.cpp

void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   ArgStringList CmdArgs;
 
   auto &TC = static_cast<const toolchains::BareMetal&>(getToolChain());
 
   AddLinkerInputs(TC, Inputs, Args, CmdArgs, JA);
 
   CmdArgs.push_back("-Bstatic");
 
-  CmdArgs.push_back(Args.MakeArgString("-L" + TC.getRuntimesDir()));
-
-  TC.AddFilePathLibArgs(Args, CmdArgs);
   Args.AddAllArgs(CmdArgs, {options::OPT_L, options::OPT_T_Group,
                             options::OPT_e, options::OPT_s, options::OPT_t,
                             options::OPT_Z_Flag, options::OPT_r});
 
+  TC.AddFilePathLibArgs(Args, CmdArgs);
+
+  CmdArgs.push_back(Args.MakeArgString("-L" + TC.getRuntimesDir()));
+
   if (TC.ShouldLinkCXXStdlib(Args))
     TC.AddCXXStdlibLibArgs(Args, CmdArgs);
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     CmdArgs.push_back("-lc");
     CmdArgs.push_back("-lm");
 
     TC.AddLinkRuntimeLib(Args, CmdArgs);
   }
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
 
   C.addCommand(std::make_unique<Command>(JA, *this, ResponseFileSupport::None(),
                                          Args.MakeArgString(TC.GetLinkerPath()),
                                          CmdArgs, Inputs, Output));
 }

clang/test/Driver/baremetal-sysroot.cpp

 // REQUIRES: shell
 // UNSUPPORTED: system-windows
 
+// Test that --sysroot always comes after any library paths.
+
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -target armv6m-none-eabi -fuse-ld=lld \
+// RUN:     -resource-dir=%S/Inputs/resource_dir \
+// RUN:     --sysroot=%S/sys-root -L%S/lib \
+// RUN:   | FileCheck --check-prefix=CHECK-V6M -DLIB_DIR=%S/lib %s
+// CHECK-V6M: "{{.*}}clang{{.*}}" "-cc1" "-triple" "thumbv6m-none-unknown-eabi"
+// CHECK-V6M-SAME: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
+// CHECK-V6M-SAME: "-isysroot" "[[SYSROOT:[^"]+]]"
+// CHECK-V6M-NEXT: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"
+// CHECK-V6M-SAME: "-L[[LIB_DIR]]"
+// CHECK-V6M-SAME: "-L[[SYSROOT]]{{/|\\\\}}lib"
+// CHECK-V6M-SAME: "-L[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}baremetal"
+// CHECK-V6M-SAME: "-lc" "-lm" "-lclang_rt.builtins-armv6m"
+// CHECK-V6M-SAME: "-o" "{{.*}}.o"
+
 // Test that when a --sysroot is not provided, driver picks the default
 // location correctly if available.
 
 // RUN: rm -rf %T/baremetal_default_sysroot
 // RUN: mkdir -p %T/baremetal_default_sysroot/bin
 // RUN: mkdir -p %T/baremetal_default_sysroot/lib/clang-runtimes/armv6m-none-eabi
 // RUN: ln -s %clang %T/baremetal_default_sysroot/bin/clang
 
 // RUN: %T/baremetal_default_sysroot/bin/clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target armv6m-none-eabi \
-// RUN:   | FileCheck --check-prefix=CHECK-V6M-C %s
-// CHECK-V6M-C: "{{.*}}clang{{.*}}" "-cc1" "-triple" "thumbv6m-none-unknown-eabi"
-// CHECK-V6M-C-SAME: "-internal-isystem" "{{.*}}/baremetal_default_sysroot{{[/\\]+}}bin{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}clang-runtimes{{[/\\]+}}armv6m-none-eabi{{[/\\]+}}include{{[/\\]+}}c++{{[/\\]+}}v1"
-// CHECk-V6M-C-SAME: "-internal-isystem" "{{.*}}/baremetal_default_sysroot{{[/\\]+}}bin{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}clang-runtimes{{[/\\]+}}armv6m-none-eabi{{[/\\]+}}include"
-// CHECK-V6M-C-SAME: "-x" "c++" "{{.*}}baremetal-sysroot.cpp"
-// CHECK-V6M-C-NEXT: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"
-// CHECK-V6M-C-SAME: "-L{{.*}}/baremetal_default_sysroot{{[/\\]+}}bin{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}clang-runtimes{{[/\\]+}}armv6m-none-eabi{{[/\\]+}}lib"
-// CHECK-V6M-C-SAME: "-lc" "-lm" "-lclang_rt.builtins-armv6m"
-// CHECK-V6M-C-SAME: "-o" "{{.*}}.o"
+// RUN:   | FileCheck --check-prefix=CHECK-V6M-DEFAULT-SYSROOT %s
+// CHECK-V6M-DEFAULT-SYSROOT: "{{.*}}clang{{.*}}" "-cc1" "-triple" "thumbv6m-none-unknown-eabi"
+// CHECK-V6M-DEFAULT-SYSROOT-SAME: "-internal-isystem" "{{.*}}/baremetal_default_sysroot{{[/\\]+}}bin{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}clang-runtimes{{[/\\]+}}armv6m-none-eabi{{[/\\]+}}include{{[/\\]+}}c++{{[/\\]+}}v1"
+// CHECk-V6M-DEFAULT-SYSROOT-SAME: "-internal-isystem" "{{.*}}/baremetal_default_sysroot{{[/\\]+}}bin{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}clang-runtimes{{[/\\]+}}armv6m-none-eabi{{[/\\]+}}include"
+// CHECK-V6M-DEFAULT-SYSROOT-SAME: "-x" "c++" "{{.*}}baremetal-sysroot.cpp"
+// CHECK-V6M-DEFAULT-SYSROOT-NEXT: "{{[^"]*}}ld{{(\.(lld|bfd|gold))?}}{{(\.exe)?}}" "{{.*}}.o" "-Bstatic"
+// CHECK-V6M-DEFAULT-SYSROOT-SAME: "-L{{.*}}/baremetal_default_sysroot{{[/\\]+}}bin{{[/\\]+}}..{{[/\\]+}}lib{{[/\\]+}}clang-runtimes{{[/\\]+}}armv6m-none-eabi{{[/\\]+}}lib"
+// CHECK-V6M-DEFAULT-SYSROOT-SAME: "-lc" "-lm" "-lclang_rt.builtins-armv6m"
+// CHECK-V6M-DEFAULT-SYSROOT-SAME: "-o" "{{.*}}.o"