Enable generation of instruction buffer on precompilation

runtime/BUILD.gn

 # Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # TODO(zra): These build arguments should likely be moved to a gni file that is
 # included in BUILD.gn files that care about the values of the flags. For now,
 # since the GN build only happens as part of a Mojo build there is no need for
 # the indirection.
 declare_args() {
   # Instead of using is_debug, we introduce a different flag for specifying a
   # Debug build of Dart so that clients can still use a Release build of Dart
   # while themselves doing a Debug build.
   dart_debug = false
+
+  # Explicitly set the target architecture in case of precompilation. Leaving
+  # this unspecified results in automatic target architecture detection.
+  # Available options are: arm, arm64, mips, x64 and ia32
+  dart_target_arch = ""
 }
 
 config("dart_public_config") {
   include_dirs = [
     ".",
   ]
 }
 
 config("dart_config") {
   defines = []
+
+  if (dart_target_arch != "") {
+    if (dart_target_arch == "arm") {
+      defines += [ "TARGET_ARCH_ARM" ]
+    } else if (dart_target_arch == "arm64") {
+      defines += [ "TARGET_ARCH_ARM64" ]
+    } else if (dart_target_arch == "mips") {
+      defines += [ "TARGET_ARCH_MIPS" ]
+    } else if (dart_target_arch == "x64") {
+      defines += [ "TARGET_ARCH_X64" ]
+    } else if (dart_target_arch == "ia32") {
+      defines += [ "TARGET_ARCH_IA32" ]
+    } else  {
+      print("Invalid |dart_target_arch|")
+      assert(false)
+    }
+  }
+
   if (dart_debug) {
     defines += ["DEBUG"]
   } else {
     defines += ["NDEBUG"]
   }
 
   cflags = [
     "-Werror",
     "-Wall",
     "-Wextra", # Also known as -W.
@@ skipping 87 matching lines @@
     "vm:libdart_lib_nosnapshot",
     "vm:libdart_lib",
     "vm:libdart_vm",
     "vm:libdart_platform",
     "third_party/double-conversion/src:libdouble_conversion",
   ]
   sources = [
     "vm/libdart_dependency_helper.cc",
   ]
 }