Turn off lldb debug tuning by default for FreeBSD

[dim]

Summary

This is the clang part of D15966. In rL256104, debugger tuning was
added to the clang driver, and again the default for FreeBSD was set to
lldb. The default needs to be gdb instead.

[emaste]

I advocated for the lldb tuning by default on FreeBSD originally, but I didn't fully understand the implications. It turns out we're just not ready yet. So, LGTM.

[probinson]

Sure, I was just making it the same as LLVM's default.
Now that it's wired up through clang, people who want LLDB can use -glldb to get the same effect.

[emaste]

Sure, I was just making it the same as LLVM's default.

Yeah, the defaults ought to be the same; it turns out this change was just premature.

lib/Driver/ToolChains.h

public:
 
   bool UseSjLjExceptions(const llvm::opt::ArgList &Args) const override;
   bool isPIEDefault() const override;
   SanitizerMask getSupportedSanitizers() const override;
   unsigned GetDefaultDwarfVersion() const override { return 2; }
   // 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; }
-  llvm::DebuggerKind getDefaultDebuggerTuning() const override {
-    return llvm::DebuggerKind::LLDB;
-  }
 
 protected:
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
 };
 
 class LLVM_LIBRARY_VISIBILITY NetBSD : public Generic_ELF {
 public:

test/Driver/debug-options.c

 // RUN: %clang -### -c -ggdb %s -target x86_64-apple-darwin 2>&1 \
 // RUN:             | FileCheck -check-prefix=G_DARWIN -check-prefix=G_GDB %s
 // RUN: %clang -### -c -ggdb1 %s -target x86_64-apple-darwin 2>&1 \
 // RUN:             | FileCheck -check-prefix=GLTO_ONLY_DWARF2 %s
 // RUN: %clang -### -c -ggdb3 %s -target x86_64-apple-darwin 2>&1 \
 // RUN:             | FileCheck -check-prefix=G_DARWIN %s
 
 // RUN: %clang -### -c -g %s -target x86_64-pc-freebsd10.0 2>&1 \
-// RUN:             | FileCheck -check-prefix=G_LLDB %s
+// RUN:             | FileCheck -check-prefix=G_GDB %s
 
 // On the PS4, -g defaults to -gno-column-info, and we always generate the
 // arange section.
 // RUN: %clang -### -c %s -target x86_64-scei-ps4 2>&1 \
 // RUN:             | FileCheck -check-prefix=NOG_PS4 %s
 // RUN: %clang -### -c %s -g -target x86_64-scei-ps4 2>&1 \
 // RUN:             | FileCheck -check-prefix=G_PS4 %s
 // RUN: %clang -### -c %s -g -target x86_64-scei-ps4 2>&1 \