Add forward instruction declaration to Subzero bitcode reader.

tests_lit/lit.cfg

Index: tests_lit/lit.cfg
diff --git a/tests_lit/lit.cfg b/tests_lit/lit.cfg
index 5e94f1e65e934778af670e5f2efd1b20a4948eb7..f1d3c7410d5b4ff595624dc59a98e25a77d3826a 100644
--- a/tests_lit/lit.cfg
+++ b/tests_lit/lit.cfg
@@ -48,7 +48,8 @@ config.substitutions.append(('%llvm2ice', llvm2icetool))
 config.substitutions.append(('%szdiff', os.path.join(pydir, 'szdiff.py')))
 
 llvmbintools = [r"\bFileCheck\b", r"\bllvm-as\b", r"\bllvm-mc\b",
-                r"\bllvm-objdump\b", r"\bnot\b", r"\bpnacl-freeze\b"]
+                r"\bllvm-objdump\b", r"\bnot\b", r"\bpnacl-freeze\b",
+                r"\bpnacl-bcdis\b"]
 
 for tool in llvmbintools:
   # The re.sub() line is adapted from one of LLVM's lit.cfg files.