[RISCV] Integrate RISCV target in baremetal toolchain object and deprecate RISCVToolchain object (#121831)

This patch:
- Adds CXXStdlib, runtimelib defaults for riscv target to
  BareMetal toolchain object.
- Set the unwindlib to None for riscv target to match the
   behavior of RISCVToolChain.
- Removes call to RISCVToolChain object from llvm.

This PR is last patch in the series of patches of merging RISCVToolchain
object into BareMetal toolchain object.

RFC:
https://discourse.llvm.org/t/merging-riscvtoolchain-and-baremetal-toolchains/75524

Author: Garvit Gupta

clang/lib/Driver/CMakeLists.txt

@@ -76,7 +76,6 @@ add_clang_library(clangDriver
   ToolChains/OHOS.cpp
   ToolChains/OpenBSD.cpp
   ToolChains/PS4CPU.cpp
-  ToolChains/RISCVToolchain.cpp
   ToolChains/Solaris.cpp
   ToolChains/SPIRV.cpp
   ToolChains/SPIRVOpenMP.cpp

clang/lib/Driver/Driver.cpp

@@ -43,7 +43,6 @@
 #include "ToolChains/PPCFreeBSD.h"
 #include "ToolChains/PPCLinux.h"
 #include "ToolChains/PS4CPU.h"
-#include "ToolChains/RISCVToolchain.h"
 #include "ToolChains/SPIRV.h"
 #include "ToolChains/SPIRVOpenMP.h"
 #include "ToolChains/SYCL.h"
@@ -6955,16 +6954,11 @@ const ToolChain &Driver::getToolChain(const ArgList &Args,
         TC = std::make_unique<toolchains::AVRToolChain>(*this, Target, Args);
         break;
       case llvm::Triple::msp430:
-        TC =
-            std::make_unique<toolchains::MSP430ToolChain>(*this, Target, Args);
+        TC = std::make_unique<toolchains::MSP430ToolChain>(*this, Target, Args);
         break;
       case llvm::Triple::riscv32:
       case llvm::Triple::riscv64:
-        if (toolchains::RISCVToolChain::hasGCCToolchain(*this, Args))
-          TC =
-              std::make_unique<toolchains::RISCVToolChain>(*this, Target, Args);
-        else
-          TC = std::make_unique<toolchains::BareMetal>(*this, Target, Args);
+        TC = std::make_unique<toolchains::BareMetal>(*this, Target, Args);
         break;
       case llvm::Triple::ve:
         TC = std::make_unique<toolchains::VEToolChain>(*this, Target, Args);

clang/lib/Driver/ToolChains/BareMetal.cpp

@@ -375,6 +375,28 @@ BareMetal::OrderedMultilibs BareMetal::getOrderedMultilibs() const {
   return llvm::reverse(Default);
 }
 
+ToolChain::CXXStdlibType BareMetal::GetDefaultCXXStdlibType() const {
+  if (getTriple().isRISCV() && IsGCCInstallationValid)
+    return ToolChain::CST_Libstdcxx;
+  return ToolChain::CST_Libcxx;
+}
+
+ToolChain::RuntimeLibType BareMetal::GetDefaultRuntimeLibType() const {
+  if (getTriple().isRISCV() && IsGCCInstallationValid)
+    return ToolChain::RLT_Libgcc;
+  return ToolChain::RLT_CompilerRT;
+}
+
+// TODO: Add a validity check for GCCInstallation.
+//       If valid, use `UNW_Libgcc`; otherwise, use `UNW_None`.
+ToolChain::UnwindLibType
+BareMetal::GetUnwindLibType(const llvm::opt::ArgList &Args) const {
+  if (getTriple().isRISCV())
+    return ToolChain::UNW_None;
+
+  return ToolChain::GetUnwindLibType(Args);
+}
+
 void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                           ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdinc))

clang/lib/Driver/ToolChains/BareMetal.h

@@ -56,13 +56,11 @@ class LLVM_LIBRARY_VISIBILITY BareMetal : public Generic_ELF {
     return UnwindTableLevel::None;
   }
 
-  RuntimeLibType GetDefaultRuntimeLibType() const override {
-    return ToolChain::RLT_CompilerRT;
-  }
+  CXXStdlibType GetDefaultCXXStdlibType() const override;
 
-  CXXStdlibType GetDefaultCXXStdlibType() const override {
-    return ToolChain::CST_Libcxx;
-  }
+  RuntimeLibType GetDefaultRuntimeLibType() const override;
+
+  UnwindLibType GetUnwindLibType(const llvm::opt::ArgList &Args) const override;
 
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,