Fix typo in lib/safestack/CMakeLists.txt that prevents safestack static library from being built on OS X.

llvm-svn: 245438
diff --git a/compiler-rt/lib/safestack/CMakeLists.txt b/compiler-rt/lib/safestack/CMakeLists.txt
index a958470..bf843ff 100644
--- a/compiler-rt/lib/safestack/CMakeLists.txt
+++ b/compiler-rt/lib/safestack/CMakeLists.txt
@@ -11,7 +11,7 @@
   foreach (os osx)
     add_compiler_rt_darwin_runtime(clang_rt.safestack_${os} ${os}
       STATIC
-      ARCH ${SAFESTACK_SUPPORTED_ARCH}
+      ARCHS ${SAFESTACK_SUPPORTED_ARCH}
       SOURCES ${SAFESTACK_SOURCES}
               $<TARGET_OBJECTS:RTInterception.${os}>
               $<TARGET_OBJECTS:RTSanitizerCommon.${os}>