Improve and simplify removal of unreachable code

tools/gyp/v8.gyp

Index: tools/gyp/v8.gyp
diff --git a/tools/gyp/v8.gyp b/tools/gyp/v8.gyp
index 5a2a22c3cdcf5aec5463fd05754706c9bff93270..846472dc2dc5d7dd6852f1525e314cd2a4e551bb 100644
--- a/tools/gyp/v8.gyp
+++ b/tools/gyp/v8.gyp
@@ -340,8 +340,6 @@
         '../../src/hydrogen-dce.h',
         '../../src/hydrogen-dehoist.cc',
         '../../src/hydrogen-dehoist.h',
-        '../../src/hydrogen-deoptimizing-mark.cc',
-        '../../src/hydrogen-deoptimizing-mark.h',
         '../../src/hydrogen-environment-liveness.cc',
         '../../src/hydrogen-environment-liveness.h',
         '../../src/hydrogen-escape-analysis.cc',
@@ -360,6 +358,8 @@
         '../../src/hydrogen-load-elimination.h',
         '../../src/hydrogen-mark-deoptimize.cc',
         '../../src/hydrogen-mark-deoptimize.h',
+        '../../src/hydrogen-mark-unreachable.cc',
+        '../../src/hydrogen-mark-unreachable.h',
         '../../src/hydrogen-minus-zero.cc',
         '../../src/hydrogen-minus-zero.h',
         '../../src/hydrogen-osr.cc',
@@ -402,6 +402,8 @@
         '../../src/lithium-allocator-inl.h',
         '../../src/lithium-allocator.cc',
         '../../src/lithium-allocator.h',
+        '../../src/lithium-codegen.cc',
+        '../../src/lithium-codegen.h',
         '../../src/lithium.cc',
         '../../src/lithium.h',
         '../../src/liveedit.cc',