Restore LLVM_BUILD_RUNTIME option that was deleted in r191835, but is still...

Restore LLVM_BUILD_RUNTIME option that was deleted in r191835, but is still used to control building of compiler-rt and libcxx

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191948 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -253,6 +253,8 @@ option(LLVM_INCLUDE_TOOLS "Generate build targets for the LLVM tools." ON)
 option(LLVM_BUILD_TOOLS
   "Build the LLVM tools. If OFF, just generate build targets." ON)
 
+option(LLVM_BUILD_RUNTIME
+  "Build the LLVM runtime libraries." ON)
 option(LLVM_BUILD_EXAMPLES
   "Build the LLVM example programs. If OFF, just generate build targets." OFF)
 option(LLVM_INCLUDE_EXAMPLES "Generate build targets for the LLVM examples" ON)