Allow Subzero to parse function blocks in parallel.

src/IceClFlags.def

Index: src/IceClFlags.def
diff --git a/src/IceClFlags.def b/src/IceClFlags.def
index 684fcb8c24ed5b57c4c4f49c0aa2bd33ce117063..45a8b41aafbe1704985cd2aba7ef5b94bac76188 100644
--- a/src/IceClFlags.def
+++ b/src/IceClFlags.def
@@ -191,6 +191,9 @@ struct dev_list_flag {};
                    "Low-level integrated assembly ('.s') file"),               \
         clEnumValEnd))                                                         \
                                                                                \
+  X(ParseParallel, bool, dev_opt_flag, "parse-parallel",                       \
+    cl::desc("Parse function blocks in parallel"), cl::init(true))             \
+                                                                               \
   X(RandomizeAndPoolImmediatesOption, Ice::RandomizeAndPoolImmediatesEnum,     \
     dev_opt_flag, "randomize-pool-immediates",                                 \
     cl::desc("Randomize or pooling the representation of immediates"),         \