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

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index f74aea74f36366a979a48abe3d1296aaba7fe1be..4d91cbfce272d0f5db9c0e84d4b80be79a45818f 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -867,6 +867,9 @@ source_set("v8_base") {
     "src/compiler/value-numbering-reducer.h",
     "src/compiler/verifier.cc",
     "src/compiler/verifier.h",
+    "src/compiler/wasm-compiler.cc",
+    "src/compiler/wasm-compiler.h",
+    "src/compiler/wasm-linkage.cc",
     "src/compiler/zone-pool.cc",
     "src/compiler/zone-pool.h",
     "src/compiler.cc",
@@ -1282,6 +1285,24 @@ source_set("v8_base") {
     "src/version.h",
     "src/vm-state-inl.h",
     "src/vm-state.h",
+    "src/wasm/asm-wasm-builder.cc",
+    "src/wasm/asm-wasm-builder.h",
+    "src/wasm/ast-decoder.cc",
+    "src/wasm/ast-decoder.h",
+    "src/wasm/decoder.h",
+    "src/wasm/encoder.cc",
+    "src/wasm/encoder.h",
+    "src/wasm/module-decoder.cc",
+    "src/wasm/module-decoder.h",
+    "src/wasm/wasm-js.cc",
+    "src/wasm/wasm-js.h",
+    "src/wasm/wasm-macro-gen.h",
+    "src/wasm/wasm-module.cc",
+    "src/wasm/wasm-module.h",
+    "src/wasm/wasm-opcodes.cc",
+    "src/wasm/wasm-opcodes.h",
+    "src/wasm/wasm-result.cc",
+    "src/wasm/wasm-result.h",
     "src/zone.cc",
     "src/zone.h",
     "src/zone-allocator.h",