Adds tls_edit utility which patches irt_core.nexe's TLS usage.

src/untrusted/irt/nacl.scons

Index: src/untrusted/irt/nacl.scons
diff --git a/src/untrusted/irt/nacl.scons b/src/untrusted/irt/nacl.scons
index df60f369d98e9270bff9abc222110c10103981e2..fc79d66d26abbcec385b7f57173489e766181129 100644
--- a/src/untrusted/irt/nacl.scons
+++ b/src/untrusted/irt/nacl.scons
@@ -69,14 +69,6 @@ irt_support_objs += [
         '${MAIN_DIR}/src/untrusted/valgrind/dynamic_annotations.c'),
     ]
 
-if env.Bit('target_arm'):
-  read_tp_obj = blob_env.ComponentObject('aeabi_read_tp.o', 'aeabi_read_tp.S')
-  irt_support_objs.append(read_tp_obj)
-  # Publish the object file for tests/irt_private_pthread to use.
-  # Putting aeabi_read_tp.o into libirt_support_private is not
-  # sufficient because of link ordering issues.
-  env.Replicate('${STAGING_DIR}', read_tp_obj)
-
 # Build a library so that irt_support_objs can be used in tests that
 # cover IRT-internal code.
 env.ComponentLibrary('libirt_support_private', irt_support_objs)
@@ -92,8 +84,28 @@ irt_libs = ['srpc',
             'm',
             ]
 
-irt_core_library = blob_env.ComponentProgram(
-    'irt_core', irt_support_objs + irt_nonbrowser, EXTRA_LIBS=irt_libs)
+irt_core_raw = blob_env.ComponentProgram(
+    'irt_core_raw', irt_support_objs + irt_nonbrowser, EXTRA_LIBS=irt_libs)
+
+# Compile this program using the host environment instead of the target
+tls_edit_env = env['BUILD_ENV']
+tls_edit_exe = tls_edit_env.ComponentProgram(
+    'tls_edit',
+    'tls_edit.c',
+    EXTRA_LIBS=['rdfa_validator', 'platform'])
+
+tls_edit_library = tls_edit_env.Install('${STAGING_DIR}', tls_edit_exe)
+
+irt_core_nexe = blob_env.Command(
+    'irt_core.nexe',
+    [tls_edit_library, irt_core_raw],
+    '${SOURCES} ${TARGET}'
+    )
+
+irt_core_library = blob_env.Install('${STAGING_DIR}', irt_core_nexe)
+blob_env.Alias('irt_core', irt_core_library)
+blob_env.ComponentProgramAlias(irt_core_library)
+
 env.SDKInstallBin('irt_core.nexe', irt_core_library)
 
 # TODO(mcgrathr): these should be installed, but scons is a mystery