[scudo] Add -fsanitize=scudo option to Fuchsia.

[flowerhack]

Summary

Apparently the -fsanitize flag hadn't been added for Scudo upstream yet. Whups!

Let me know if there are more comprehensive tests I should be adding~

[cryptoad]

As discussed: you probably want to enforce mutual exclusion of the sanitizers (eg: ASan is not compatible with Scudo).
I have not test Scudo+Safestack but they should be compatible (or at least with a small amount of work can should be made to be).

[mcgrathr]

Mutual exclusion is not target-specific and is already handled in SanitizerArgs. The test coverage for that looks fine.

test/Driver/fuchsia.c

99

Never have a file that does not end with a newline.

[phosek]

LGTM % nits

test/Driver/fuchsia.c

83

Can you use just the tuple triple target form, i.e. x86_64-fuchsia? We should cleanup the rest of the file to use the same format but I'll do that in a separate change.

lib/Driver/ToolChains/Fuchsia.cpp

case ToolChain::CST_Libstdcxx:
     llvm_unreachable("invalid stdlib name");
   }
 }
 
 SanitizerMask Fuchsia::getSupportedSanitizers() const {
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::SafeStack;
   Res |= SanitizerKind::Address;
+  Res |= SanitizerKind::Scudo;
   return Res;
 }

test/Driver/fuchsia.c

 
 // RUN: %clang %s -### --target=x86_64-unknown-fuchsia \
 // RUN:     -fsanitize=address -fPIC -shared 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-ASAN-SHARED
 // 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=scudo 2>&1 \
+// RUN:     | FileCheck %s -check-prefix=CHECK-SCUDO-X86
+// CHECK-SCUDO-X86: "-fsanitize=scudo"
+// CHECK-SCUDO-X86: "-pie"
+
+// 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: "-pie"
+
+// 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"