Subzero: Update for LLVM 3.9 (trunk).

The purpose is to allow pnacl-sz to be built within an LLVM checkout (version 3.9 or later), and not require the complex PNaCl build environment.

Within an LLVM checkout, one would do something like the following:
  cd projects
  git clone https://chromium.googlesource.com/native_client/pnacl-subzero
  # change to LLVM build directory
  cmake -G "Ninja" <path_to_llvm_source_dir>
  ninja

A follow-on CL will add in the PNaCl bitcode reader source files that are needed for compiling and linking.

BUG= none
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1961743002 .
diff --git a/Makefile.standalone b/Makefile.standalone
index deb8ab5..d6bfb8e 100644
--- a/Makefile.standalone
+++ b/Makefile.standalone
@@ -110,6 +110,8 @@
   BASE_CXX_DEFINES += -DSZTARGET=$(SZTARGET)
 endif
 
+BASE_CXX_DEFINES += -DPNACL_LLVM
+
 CXX_DEFINES := $(BASE_CXX_DEFINES) -DPNACL_BROWSER_TRANSLATOR=0
 
 ifdef NOASSERT