[clang] [MinGW] Default to DWARF 4

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

This applies the same change as in
9c62728 (Default to DWARFv4 on Windows)
to the MinGW driver too.

Differential Revision: https://reviews.llvm.org/D119326

(cherry picked from commit 6cf64b2)

Author: mstorsjo

clang/lib/Driver/ToolChains/MinGW.h

@@ -90,6 +90,8 @@ class LLVM_LIBRARY_VISIBILITY MinGW : public ToolChain {
 
   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;

clang/test/CodeGen/dwarf-version.c

@@ -32,6 +32,11 @@
 //     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 | \