Subzero: Run cross tests as a much more configurable python script.

crosstest/crosstest.cfg

+[simple_loop]
+driver: simple_loop_main.c
+test: simple_loop.c
+
+[mem_intrin]
+driver: mem_intrin_main.cpp
+test: mem_intrin.cpp
+
+[test_arith]
+driver: test_arith_main.cpp
+test: test_arith.cpp test_arith_frem.ll test_arith_sqrt.ll
+
+[test_bitmanip]
+driver: test_bitmanip_main.cpp
+test: test_bitmanip.cpp test_bitmanip_intrin.ll
+
+[test_calling_conv]
+driver: test_calling_conv_main.cpp
+test: test_calling_conv.cpp
+
+[test_cast]
+driver: test_cast_main.cpp
+test: test_cast.cpp test_cast_to_u1.ll test_cast_vectors.ll
+
+[test_fcmp]
+driver: test_fcmp_main.cpp
+test: test_fcmp.pnacl.ll
+
+[test_global]
+driver: test_global_main.cpp
+test: test_global.cpp
+
+[test_icmp]
+driver: test_icmp_main.cpp
+test: test_icmp.cpp test_icmp_i1vec.ll
+
+[test_select]
+driver: test_select_main.cpp
+test: test_select.ll
+
+[test_stacksave]
+driver: test_stacksave_main.c
+test: test_stacksave.c
+
+[test_sync_atomic]
+driver: test_sync_atomic_main.cpp
+# Compile the non-Subzero object files straight from source since the native
+# LLVM backend does not understand how to lower NaCl-specific intrinsics.
+flags: --crosstest-bitcode=0
+test: test_sync_atomic.cpp
+
+[test_vector_ops]
+driver: test_vector_ops_main.cpp
+test: test_vector_ops.ll