IRT: Replace __attribute__((constructor)) with explicit call in _start()

tests/irt_compatibility/nacl.scons

Index: tests/irt_compatibility/nacl.scons
diff --git a/tests/irt_compatibility/nacl.scons b/tests/irt_compatibility/nacl.scons
index 73cf786f0307da5b51f43fa3d91099742208bba6..5e1c4cc97ac33b11ee02a1761dff988d771a25cf 100644
--- a/tests/irt_compatibility/nacl.scons
+++ b/tests/irt_compatibility/nacl.scons
@@ -16,15 +16,12 @@ blob_env = env['NACL_IRT_ENV'].Clone()
 blob_env.Append(LINKFLAGS=[blob_env.RodataSwitch('${IRT_BLOB_DATA_START}'),
                            blob_env.TextSwitch('${IRT_BLOB_CODE_START}')])
 
-irt_entry_obj = blob_env.ComponentObject(
-    '${MAIN_DIR}/src/untrusted/irt/irt_entry.c')
-
 # Build custom IRT library which provides a minimal subset of old
 # interface versions.
 blob_env.Append(CPPDEFINES=[['ALLOW_DYNAMIC_LINKING',
                              str(int(not env.Bit('nacl_static_link')))]])
 irt_comp_test_library = blob_env.ComponentProgram(
-    'irt_comp_test', [irt_entry_obj, 'irt_comp_interfaces.c'],
+    'irt_comp_test', ['irt_comp_interfaces.c'],
     EXTRA_LIBS=['irt_support_private'])
 
 # Don't provide IRT, we provide it ourselves via -B.