[Fuchsia][CMake] Update OSX deployment target

Use correct spelling of CMAKE_OSX_DEPLOYMENT_TARGET and bump the
minimum version to 10.13 which matches what we use for host tools
in Fuchsia.

Differential Revision: https://reviews.llvm.org/D102013
diff --git a/clang/cmake/caches/Fuchsia-stage2.cmake b/clang/cmake/caches/Fuchsia-stage2.cmake
index f83ef1f..2cc25ba 100644
--- a/clang/cmake/caches/Fuchsia-stage2.cmake
+++ b/clang/cmake/caches/Fuchsia-stage2.cmake
@@ -42,7 +42,7 @@
 
 set(CMAKE_BUILD_TYPE Release CACHE STRING "")
 if (APPLE)
-  set(MACOSX_DEPLOYMENT_TARGET 10.7 CACHE STRING "")
+  set(CMAKE_OSX_DEPLOYMENT_TARGET "10.13" CACHE STRING "")
 elseif(MSVC)
   set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded" CACHE STRING "")
 endif()
diff --git a/clang/cmake/caches/Fuchsia.cmake b/clang/cmake/caches/Fuchsia.cmake
index d61b5e6..92097da 100644
--- a/clang/cmake/caches/Fuchsia.cmake
+++ b/clang/cmake/caches/Fuchsia.cmake
@@ -36,7 +36,7 @@
 set(LLVM_ENABLE_ASSERTIONS ON CACHE BOOL "")
 set(CMAKE_BUILD_TYPE Release CACHE STRING "")
 if(APPLE)
-  set(MACOSX_DEPLOYMENT_TARGET 10.7 CACHE STRING "")
+  set(CMAKE_OSX_DEPLOYMENT_TARGET "10.13" CACHE STRING "")
 elseif(MSVC)
   set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded" CACHE STRING "")
 endif()