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

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 a9aa6b21fab1d375c69168da24409dbafa5329e6..9d778d7eaf705d97e7c37aa5e8a8068c24d37dbf 100644
--- a/tests/irt_compatibility/nacl.scons
+++ b/tests/irt_compatibility/nacl.scons
@@ -20,10 +20,18 @@ blob_env.Append(LINKFLAGS=['-Wl,-Trodata-segment=${IRT_BLOB_DATA_START}',
 # 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_comp_interfaces.c'],
+irt_comp_test_raw_library = blob_env.ComponentProgram(
+    'irt_comp_test_raw', ['irt_comp_interfaces.c'],
     EXTRA_LIBS=['irt_support_private'])
 
+tls_edit_exe = env.GetTLSEdit()
+
+irt_comp_test_library = env.Command(
+    'irt_comp_test',
+    [tls_edit_exe, irt_comp_test_raw_library],
+    '${SOURCES} ${TARGET}'
+    )
+
 # Don't provide IRT, we provide it ourselves via -B.
 env.ClearBits('tests_use_irt')