Revert of Remove wasm compile time option and enable wasm behind a runtime flag.

test/unittests/unittests.gyp

Index: test/unittests/unittests.gyp
diff --git a/test/unittests/unittests.gyp b/test/unittests/unittests.gyp
index 2c768a042b7cc9c2b35a7a0bb831b61736b9aab7..a905b7dace700cd2b20b4ae10e252a7a3096eecc 100644
--- a/test/unittests/unittests.gyp
+++ b/test/unittests/unittests.gyp
@@ -110,10 +110,6 @@
         'runtime/runtime-interpreter-unittest.cc',
         'test-utils.h',
         'test-utils.cc',
-        'wasm/ast-decoder-unittest.cc',
-        'wasm/encoder-unittest.cc',
-        'wasm/module-decoder-unittest.cc',
-        'wasm/wasm-macro-gen-unittest.cc',
       ],
       'conditions': [
         ['v8_target_arch=="arm"', {
@@ -172,6 +168,14 @@
               '-pedantic',
             ],
           },
+        }],
+        ['v8_wasm!=0', {
+          'sources': [
+            'wasm/ast-decoder-unittest.cc',
+            'wasm/encoder-unittest.cc',
+            'wasm/module-decoder-unittest.cc',
+            'wasm/wasm-macro-gen-unittest.cc',
+          ],
         }],
       ],
     },