Windows GN build flag fixes.

This brings some more flags in line with the GYP build on Windows. In particular, this ads the SSE2 flag on x86, and the stack linker flag on x64.

Review-Url: https://codereview.chromium.org/2077173002
Cr-Commit-Position: refs/heads/master@{#37114}

BUILD.gn

@@ -164,6 +164,7 @@ config("toolchain") {
 
   defines = []
   cflags = []
+  ldflags = []
 
   if (v8_target_cpu == "arm") {
     defines += [ "V8_TARGET_ARCH_ARM" ]
@@ -269,16 +270,22 @@ config("toolchain") {
   }
   if (v8_target_cpu == "x86") {
     defines += [ "V8_TARGET_ARCH_IA32" ]
+    if (is_win) {
+      # Ensure no surprising artifacts from 80bit double math with x86.
+      cflags += [ "/arch:SSE2" ]
+    }
   }
   if (v8_target_cpu == "x64") {
     defines += [ "V8_TARGET_ARCH_X64" ]
+    if (is_win) {
+      # Increase the initial stack size. The default is 1MB, this is 2MB. This
+      # applies only to executables and shared libraries produced by V8 since
+      # ldflags are not pushed to dependants.
+      ldflags += [ "/STACK:2097152" ]
+    }
   }
 
-  if (is_win) {
-    defines += [ "WIN32" ]
-    # TODO(jochen): Support v8_enable_prof.
-  }
-
+  # TODO(jochen): Support v8_enable_prof on Windows.
   # TODO(jochen): Add support for compiling with simulators.
 
   if (is_debug) {