Always output zero-terminator in slangdata.py.

Output one more byte '\0' can be useful when the input data file is
a bitcode file. With the existence of '\0', we can use

        llvm::MemoryBuffer::getMemBuffer()

                    instead of

        llvm::MemoryBuffer::getMemBufferCopy()

to prepare buffer for llvm::ParseBitcodeFile(llvm::MemoryBuffer, ...).
diff --git a/llvm-rs-link.cpp b/llvm-rs-link.cpp
index 20d3669..32ea36d 100644
--- a/llvm-rs-link.cpp
+++ b/llvm-rs-link.cpp
@@ -145,8 +145,8 @@
 
   if (!NoStdLib) {
     // rslib.bc
-    MB = MemoryBuffer::getMemBufferCopy(StringRef(rslib_bc, rslib_bc_size),
-                                        "rslib.bc");
+    MB = MemoryBuffer::getMemBuffer(StringRef(rslib_bc, rslib_bc_size),
+                                    "rslib.bc");
     if (MB == NULL) {
       errs() << "Failed to load (in-memory) `rslib.bc'!\n";
       return false;