[RISCV] Disable generation of asynchronous unwind tables for RISCV baremetal

The below culprit patch enabled the generation of asynchronous unwind tables
(-funwind-tables=2) by default for RISCV for both linux and RISCVToolChain
baremetal object. However, since there are 2 baremetal toolchain objects for
RISCV, this created a discrepancy between their behavior. Moreover, enabling
the generation of asynchronous unwind tables based on whether `-gcc-toolchain`
option is present or not doesn't seem to be the best criteria to decide on
the same.

Culprit Patch - https://reviews.llvm.org/D145164

Author: quic-garvgupt

clang/lib/Driver/ToolChains/RISCVToolchain.cpp

@@ -86,6 +86,11 @@ RISCVToolChain::GetUnwindLibType(const llvm::opt::ArgList &Args) const {
   return ToolChain::UNW_None;
 }
 
+ToolChain::UnwindTableLevel RISCVToolChain::getDefaultUnwindTableLevel(
+    const llvm::opt::ArgList &Args) const {
+  return UnwindTableLevel::None;
+}
+
 void RISCVToolChain::addClangTargetOptions(
     const llvm::opt::ArgList &DriverArgs,
     llvm::opt::ArgStringList &CC1Args,

clang/lib/Driver/ToolChains/RISCVToolchain.h

@@ -28,6 +28,8 @@ class LLVM_LIBRARY_VISIBILITY RISCVToolChain : public Generic_ELF {
   RuntimeLibType GetDefaultRuntimeLibType() const override;
   UnwindLibType
   GetUnwindLibType(const llvm::opt::ArgList &Args) const override;
+  UnwindTableLevel
+  getDefaultUnwindTableLevel(const llvm::opt::ArgList &Args) const override;
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;

clang/test/Driver/clang-translation.c

@@ -421,3 +421,11 @@
 // MIPSN32R6EL: "-target-cpu" "mips64r6"
 // MIPSN32R6EL: "-target-abi" "n32"
 // MIPSN32R6EL: "-mfloat-abi" "hard"
+
+// RUN: %clang --target=riscv32-unknown-elf --gcc-toolchain="" -### %s 2>&1 | FileCheck %s -check-prefix=NOUWTABLE
+// RUN: %clang --target=riscv32-unknown-elf --gcc-toolchain="" -fasynchronous-unwind-tables -### %s 2>&1 | FileCheck %s -check-prefix=UWTABLE
+// RUN: %clang --target=riscv64-unknown-elf --gcc-toolchain="" -### %s 2>&1 | FileCheck %s -check-prefix=NOUWTABLE
+// RUN: %clang --target=riscv64-unknown-elf --gcc-toolchain="" -fasynchronous-unwind-tables -### %s 2>&1 | FileCheck %s -check-prefix=UWTABLE
+//
+// UWTABLE: "-funwind-tables=2"
+// NOUWTABLE-NOT: "-funwind-tables=2"