[Fuchsia] Use thread-pointer ABI slots for stack-protector and safe-stack

The Fuchsia ABI defines slots from the thread pointer where the
stack-guard value for stack-protector, and the unsafe stack pointer
for safe-stack, are stored. This parallels the Android ABI support.

Patch by Roland McGrath

Differential Revision: https://reviews.llvm.org/D30237

llvm-svn: 296081
diff --git a/llvm/lib/Target/X86/X86Subtarget.h b/llvm/lib/Target/X86/X86Subtarget.h
index 75b87a0..1218d98 100644
--- a/llvm/lib/Target/X86/X86Subtarget.h
+++ b/llvm/lib/Target/X86/X86Subtarget.h
@@ -518,6 +518,7 @@
   bool isTargetNaCl32() const { return isTargetNaCl() && !is64Bit(); }
   bool isTargetNaCl64() const { return isTargetNaCl() && is64Bit(); }
   bool isTargetMCU() const { return TargetTriple.isOSIAMCU(); }
+  bool isTargetFuchsia() const { return TargetTriple.isOSFuchsia(); }
 
   bool isTargetWindowsMSVC() const {
     return TargetTriple.isWindowsMSVCEnvironment();