Extending Baremetal toolchain's support for the rtlib option.

Differential Revision: https://reviews.llvm.org/D87164

Patch by Manuel Carrasco!

Author: jroelofs

clang/lib/Driver/ToolChains/BareMetal.cpp

@@ -156,8 +156,17 @@ void BareMetal::AddCXXStdlibLibArgs(const ArgList &Args,
 
 void BareMetal::AddLinkRuntimeLib(const ArgList &Args,
                                   ArgStringList &CmdArgs) const {
-  CmdArgs.push_back(Args.MakeArgString("-lclang_rt.builtins-" +
-                                       getTriple().getArchName()));
+  ToolChain::RuntimeLibType RLT = GetRuntimeLibType(Args);
+  switch (RLT) {
+  case ToolChain::RLT_CompilerRT:
+    CmdArgs.push_back(
+        Args.MakeArgString("-lclang_rt.builtins-" + getTriple().getArchName()));
+    return;
+  case ToolChain::RLT_Libgcc:
+    CmdArgs.push_back("-lgcc");
+    return;
+  }
+  llvm_unreachable("Unhandled RuntimeLibType.");
 }
 
 void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,

clang/test/Driver/baremetal.cpp

@@ -83,3 +83,7 @@
 // RUN: %clangxx -target arm-none-eabi -mthread-model posix -v 2>&1 \
 // RUN:   | FileCheck %s --check-prefix=CHECK-THREAD-MODEL-POSIX
 // CHECK-THREAD-MODEL-POSIX: Thread model: posix
+
+// RUN: %clang -### -target arm-none-eabi -rtlib=libgcc -v %s 2>&1 \
+// RUN:   | FileCheck %s --check-prefix=CHECK-RTLIB-GCC
+// CHECK-RTLIB-GCC: -lgcc