[clang] [MinGW] Default to DWARF 4

[mstorsjo]

Summary

Neither LLDB nor GDB seem to work with DWARF 5 debug information on
Windows right now.

This applies the same change as in
9c6272861032f511a23784ce0c5cc8f6ac2f625b (Default to DWARFv4 on Windows)
to the MinGW driver too.

[mati865]

LGTM

clang/lib/Driver/ToolChains/MinGW.h

public:
 
   void AddCudaIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                           llvm::opt::ArgStringList &CC1Args) const override;
   void AddHIPIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                          llvm::opt::ArgStringList &CC1Args) const override;
 
   void printVerboseInfo(raw_ostream &OS) const override;
 
+  unsigned GetDefaultDwarfVersion() const override { return 4; }
+
 protected:
   Tool *getTool(Action::ActionClass AC) const override;
   Tool *buildLinker() const override;
   Tool *buildAssembler() const override;
 
 private:
   CudaInstallationDetector CudaInstallation;
   RocmInstallationDetector RocmInstallation;

clang/test/CodeGen/dwarf-version.c

 // RUN: %clang -target i686-pc-windows-msvc -gcodeview -S -emit-llvm -o - %s \
 // RUN:     | FileCheck %s --check-prefixes=NODWARF,CODEVIEW
 //     Explicitly request DWARF.
 // RUN: %clang -target i686-pc-windows-msvc -gdwarf -S -emit-llvm -o - %s \
 // RUN:     | FileCheck %s --check-prefixes=VER4,NOCODEVIEW
 //     Explicitly request both.
 // RUN: %clang -target i686-pc-windows-msvc -gdwarf -gcodeview -S -emit-llvm -o - %s \
 // RUN:     | FileCheck %s --check-prefixes=VER4,CODEVIEW
+
+// Check what version of dwarf is used for MinGW targets.
+// RUN: %clang -target i686-pc-windows-gnu -g -S -emit-llvm -o - %s | \
+// RUN:   FileCheck %s --check-prefixes=VER4
+
 // RUN: %clang -target powerpc-ibm-aix-xcoff -g -S -emit-llvm -o - %s | \
 // RUN:   FileCheck %s --check-prefix=VER3
 // RUN: %clang -target powerpc-ibm-aix-xcoff -gdwarf-2 -S -emit-llvm -o - %s | \
 // RUN:   FileCheck %s --check-prefix=VER2
 // RUN: %clang -target powerpc-ibm-aix-xcoff -gdwarf-3 -S -emit-llvm -o - %s | \
 // RUN:   FileCheck %s --check-prefix=VER3
 // RUN: %clang -target powerpc-ibm-aix-xcoff -gdwarf-4 -S -emit-llvm -o - %s | \
 // RUN:   FileCheck %s --check-prefix=VER4