[Driver] Enable SafeStack by default on Fuchsia

[phosek]

Summary

This is already used throughout the entire system, so make it a default.

clang/lib/Driver/ToolChains/Fuchsia.h

public:
   llvm::DebuggerKind getDefaultDebuggerTuning() const override {
     return llvm::DebuggerKind::GDB;
   }
 
   std::string ComputeEffectiveClangTriple(const llvm::opt::ArgList &Args,
                                           types::ID InputType) const override;
 
   SanitizerMask getSupportedSanitizers() const override;
+  SanitizerMask getDefaultSanitizers() const override;
 
   RuntimeLibType
   GetRuntimeLibType(const llvm::opt::ArgList &Args) const override;
   CXXStdlibType
   GetCXXStdlibType(const llvm::opt::ArgList &Args) const override;
 
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args,

clang/lib/Driver/ToolChains/Fuchsia.cpp

 SanitizerMask Fuchsia::getSupportedSanitizers() const {
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::Address;
   Res |= SanitizerKind::Fuzzer;
   Res |= SanitizerKind::SafeStack;
   Res |= SanitizerKind::Scudo;
   return Res;
 }
+
+SanitizerMask Fuchsia::getDefaultSanitizers() const {
+  return SanitizerKind::SafeStack;
+}

clang/test/Driver/fuchsia.c

 // RUN: %clang %s -### -no-canonical-prefixes --target=x86_64-unknown-fuchsia \
 // RUN:     --sysroot=%S/platform 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-X86_64 %s
 // RUN: %clang %s -### -no-canonical-prefixes --target=aarch64-unknown-fuchsia \
 // RUN:     --sysroot=%S/platform 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-AARCH64 %s
 // CHECK: {{.*}}clang{{.*}}" "-cc1"
 // CHECK: "--mrelax-relocations"
 // CHECK: "-munwind-tables"
 // CHECK: "-fuse-init-array"
 // CHECK: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK: "-internal-externc-isystem" "[[SYSROOT]]{{/|\\\\}}include"
+// CHECK: "-fsanitize=safe-stack"
 // CHECK: "-fno-common"
 // CHECK: {{.*}}ld.lld{{.*}}" "-z" "rodynamic"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
 // CHECK: "--build-id"
 // CHECK: "--hash-style=gnu"
 // CHECK: "-dynamic-linker" "ld.so.1"
 // CHECK: Scrt1.o

 // CHECK-ASAN-SHARED: "-fsanitize=address"
 // CHECK-ASAN-SHARED: "-fsanitize-address-globals-dead-stripping"
 // CHECK-ASAN-SHARED: "{{.*[/\\]}}libclang_rt.asan-x86_64.so"
 // CHECK-ASAN-SHARED-NOT: "{{.*[/\\]}}libclang_rt.asan-preinit-x86_64.a"
 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -fsanitize=fuzzer 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-FUZZER-X86
-// CHECK-FUZZER-X86: "-fsanitize=fuzzer,fuzzer-no-link"
+// CHECK-FUZZER-X86: "-fsanitize=fuzzer,fuzzer-no-link,safe-stack"
 // CHECK-FUZZER-X86: "{{.*[/\\]}}libclang_rt.fuzzer-x86_64.a"
 
 // RUN: %clang %s -### --target=aarch64-fuchsia \
 // RUN:     -fsanitize=fuzzer 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-FUZZER-AARCH64
-// CHECK-FUZZER-AARCH64: "-fsanitize=fuzzer,fuzzer-no-link"
+// CHECK-FUZZER-AARCH64: "-fsanitize=fuzzer,fuzzer-no-link,safe-stack"
 // CHECK-FUZZER-AARCH64: "{{.*[/\\]}}libclang_rt.fuzzer-aarch64.a"
 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -fsanitize=scudo 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SCUDO-X86
-// CHECK-SCUDO-X86: "-fsanitize=scudo"
+// CHECK-SCUDO-X86: "-fsanitize=safe-stack,scudo"
 // CHECK-SCUDO-X86: "-pie"
 // CHECK-SCUDO-X86: "{{.*[/\\]}}libclang_rt.scudo-x86_64.so"
 
 // RUN: %clang %s -### --target=aarch64-fuchsia \
 // RUN:     -fsanitize=scudo 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SCUDO-AARCH64
-// CHECK-SCUDO-AARCH64: "-fsanitize=scudo"
+// CHECK-SCUDO-AARCH64: "-fsanitize=safe-stack,scudo"
 // CHECK-SCUDO-AARCH64: "-pie"
 // CHECK-SCUDO-AARCH64: "{{.*[/\\]}}libclang_rt.scudo-aarch64.so"
 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -fsanitize=scudo -fPIC -shared 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SCUDO-SHARED
-// CHECK-SCUDO-SHARED: "-fsanitize=scudo"
+// CHECK-SCUDO-SHARED: "-fsanitize=safe-stack,scudo"
 // CHECK-SCUDO-SHARED: "{{.*[/\\]}}libclang_rt.scudo-x86_64.so"