clang: default to DWARF 4 for FreeBSD 12.0 and later

[emaste]

Summary

Older FreeBSD versions included GDB 6.1 and had other tools that were unable to handle debug information newer than DWARF 2. Those tools have since been updated. (An old version of GDB is still kept for kernel crash handling, but the kernel is compiled with an explicit -gdwarf2.)

[emaste]

FreeBSD references:
https://reviews.freebsd.org/D17930
https://reviews.freebsd.org/rS343429

Note that in FreeBSD I used < 13 for the version test but all of the prereq changes were made in advance of FreeBSD 12.0.

[aprantl]

Is this testable as a driver test?

clang/lib/Driver/ToolChains/FreeBSD.cpp

368

Is getOSMAjorVersion a typo?

[emaste]

Correct typo, update tests

[emaste]

clang/test/Driver/debug-options.c

69 ↗

(On Diff #218458)

FreeBSD 10 is out of support now, so use 11 as the base case

[dim]

LGTM

clang/lib/Driver/ToolChains/FreeBSD.h

void addLibStdCxxIncludePaths(
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
 
   llvm::ExceptionHandling GetExceptionModel(
       const llvm::opt::ArgList &Args) const override;
   bool isPIEDefault() const override;
   SanitizerMask getSupportedSanitizers() const override;
-  unsigned GetDefaultDwarfVersion() const override { return 2; }
+  unsigned GetDefaultDwarfVersion() const override;
   // Until dtrace (via CTF) and LLDB can deal with distributed debug info,
   // FreeBSD defaults to standalone/full debug info.
   bool GetDefaultStandaloneDebug() const override { return true; }
 
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_FREEBSD_H

clang/lib/Driver/ToolChains/FreeBSD.cpp

 }
 
 ToolChain::CXXStdlibType FreeBSD::GetDefaultCXXStdlibType() const {
   if (getTriple().getOSMajorVersion() >= 10)
     return ToolChain::CST_Libcxx;
   return ToolChain::CST_Libstdcxx;
 }
 
+unsigned FreeBSD::GetDefaultDwarfVersion() const {
+  if (getTriple().getOSMAjorVersion() < 12)
+    return 2;
+  return 4;
+}
+
 void FreeBSD::addLibStdCxxIncludePaths(
     const llvm::opt::ArgList &DriverArgs,
     llvm::opt::ArgStringList &CC1Args) const {
   addLibStdCXXIncludePaths(getDriver().SysRoot, "/usr/include/c++/4.2", "", "",
                            "", "", DriverArgs, CC1Args);
 }
 
 void FreeBSD::AddCXXStdlibLibArgs(const ArgList &Args,