Enable SafeStack for CloudABI.

[ed]

Summary

I've got a patchset in my home directory to integrate support for
SafeStack into CloudABI's C library. All of the CloudABI unit tests
still seem to pass. Pretty sweet!

This change adds the necessary changes to Clang to make
-fsanitize=safe-stack work on CloudABI. Without it, passing this command
line flag throws an error.

[samsonov]

Please add a test case for this (probably to test/Driver/fsanitize.c).

[ed]

Also add a testcase.

[ed]

In D17243#353661, @samsonov wrote:

Please add a test case for this (probably to test/Driver/fsanitize.c).

Done!

[samsonov]

LGTM

lib/Driver/ToolChains.h

public:
   void AddClangCXXStdlibIncludeArgs(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
 
   bool isPIEDefault() const override { return false; }
 
+  SanitizerMask getSupportedSanitizers() const override;
+
 protected:
   Tool *buildLinker() const override;
 };
 
 class LLVM_LIBRARY_VISIBILITY Solaris : public Generic_GCC {
 public:
   Solaris(const Driver &D, const llvm::Triple &Triple,
           const llvm::opt::ArgList &Args);

lib/Driver/ToolChains.cpp

void CloudABI::AddCXXStdlibLibArgs(const ArgList &Args,
   CmdArgs.push_back("-lc++abi");
   CmdArgs.push_back("-lunwind");
 }
 
 Tool *CloudABI::buildLinker() const {
   return new tools::cloudabi::Linker(*this);
 }
 
+SanitizerMask CloudABI::getSupportedSanitizers() const {
+  SanitizerMask Res = ToolChain::getSupportedSanitizers();
+  Res |= SanitizerKind::SafeStack;
+  return Res;
+}
+
 /// OpenBSD - OpenBSD tool chain which can call as(1) and ld(1) directly.
 
 OpenBSD::OpenBSD(const Driver &D, const llvm::Triple &Triple,
                  const ArgList &Args)
     : Generic_ELF(D, Triple, Args) {
   getFilePaths().push_back(getDriver().Dir + "/../lib");
   getFilePaths().push_back("/usr/lib");
 }

test/Driver/fsanitize.c

 // SP: "-fsanitize=safe-stack"
 // SP-ASAN-NOT: stack-protector
 // SP-ASAN: "-fsanitize=address,safe-stack"
 
 // RUN: %clang -target powerpc64-unknown-linux-gnu -fsanitize=memory %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SANM
 // RUN: %clang -target powerpc64le-unknown-linux-gnu -fsanitize=memory %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SANM
 // CHECK-SANM: "-fsanitize=memory"
 
+// RUN: %clang -target aarch64-unknown-cloudabi -fsanitize=safe-stack %s -### 2>&1 | FileCheck %s -check-prefix=SAFESTACK-CLOUDABI
+// RUN: %clang -target x86_64-unknown-cloudabi -fsanitize=safe-stack %s -### 2>&1 | FileCheck %s -check-prefix=SAFESTACK-CLOUDABI
+// SAFESTACK-CLOUDABI: "-fsanitize=safe-stack"
+
 // RUN: %clang -target x86_64-scei-ps4 -fsanitize=function -fsanitize=undefined %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FSAN-UBSAN-PS4
 // CHECK-FSAN-UBSAN-PS4: unsupported option '-fsanitize=function' for target 'x86_64-scei-ps4'
 // RUN: %clang -target x86_64-scei-ps4 -fsanitize=function %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FSAN-PS4
 // CHECK-FSAN-PS4: unsupported option '-fsanitize=function' for target 'x86_64-scei-ps4'
 // RUN: %clang -target x86_64-scei-ps4 -fsanitize=dataflow %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-DFSAN-PS4
 // CHECK-DFSAN-PS4: unsupported option '-fsanitize=dataflow' for target 'x86_64-scei-ps4'
 // RUN: %clang -target x86_64-scei-ps4 -fsanitize=leak %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-LSAN-PS4
 // CHECK-LSAN-PS4: unsupported option '-fsanitize=leak' for target 'x86_64-scei-ps4'
 // RUN: %clang -target x86_64-scei-ps4 -fsanitize=memory %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-MSAN-PS4
 // CHECK-MSAN-PS4: unsupported option '-fsanitize=memory' for target 'x86_64-scei-ps4'
 // RUN: %clang -target x86_64-scei-ps4 -fsanitize=thread %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-TSAN-PS4
 // CHECK-TSAN-PS4: unsupported option '-fsanitize=thread' for target 'x86_64-scei-ps4'
 // RUN: %clang -target x86_64-scei-ps4 -fsanitize=address %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-ASAN-PS4
 // Make sure there are no *.{o,bc} or -l passed before the ASan library.
 // CHECK-ASAN-PS4-NOT: {{(\.(o|bc)"? |-l).*-lSceDbgAddressSanitizer_stub_weak}}
 // CHECK-ASAN-PS4: -lSceDbgAddressSanitizer_stub_weak