[Driver][FreeBSD] Enable unwind tables on !amd64

[cem]

Summary

There doesn't seem to be much sense in defaulting "on" unwind tables on
amd64 and not on other arches. It causes surprising differences between
platforms, such as the PR below.

Prior to this change, FreeBSD inherited the default implementation of the
method from the Gnu.h Generic_Elf => Generic_GCC parent class, which
returned true only for amd64 targets. Override that and opt on always,
similar to, e.g., NetBSD's driver.

A simple test case for a !amd64 architecture is added to the "freebsd.c"
tests.

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=241562

[dim]

LGTM

clang/lib/Driver/ToolChains/FreeBSD.h

public:
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       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 IsUnwindTablesDefault(const llvm::opt::ArgList &Args) const override;
   bool isPIEDefault() const override;
   SanitizerMask getSupportedSanitizers() const override;
   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:

clang/lib/Driver/ToolChains/FreeBSD.cpp

if (getTriple().getArch() == llvm::Triple::arm ||
         getTriple().getArch() == llvm::Triple::thumb)
       return llvm::ExceptionHandling::SjLj;
     return llvm::ExceptionHandling::None;
   }
 }
 
 bool FreeBSD::HasNativeLLVMSupport() const { return true; }
 
+bool FreeBSD::IsUnwindTablesDefault(const ArgList &Args) const { return true; }
+
 bool FreeBSD::isPIEDefault() const { return getSanitizerArgs().requiresPIE(); }
 
 SanitizerMask FreeBSD::getSupportedSanitizers() const {
   const bool IsX86 = getTriple().getArch() == llvm::Triple::x86;
   const bool IsX86_64 = getTriple().getArch() == llvm::Triple::x86_64;
   const bool IsMIPS64 = getTriple().isMIPS64();
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::Address;

clang/test/Driver/freebsd.c

 // RUN: %clang -target mips64el-unknown-freebsd -### -c %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-MIPS64-CPU %s
 // CHECK-MIPS64-CPU: "-target-cpu" "mips3"
 
 // Check that the integrated assembler is enabled for SPARC64
 // RUN: %clang -target sparc64-unknown-freebsd -### -c %s 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-IAS %s
 // CHECK-IAS-NOT: "-no-integrated-as"
+
+// RUN: %clang -target ppc64-unknown-freebsd13.0 -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=PPC64-MUNWIND %s
+// PPC64-MUNWIND: -munwind-table