Add SSE2/MMX build flags when building on an x86 host. This is necessary

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 2f48477b9750977c999af1c6408cdb762ebba269..a608b4a9453c237971e1edaa61b1ecb9bfaf4868 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -219,6 +219,14 @@ config("compiler") {
     }
   }
 
+  if (current_cpu == "x86") {
+    cflags += [
+      "-msse2",
+      "-mfpmath=sse",
+      "-mmmx",

[Nico, 2016/05/05 17:33:23]

doesn't msse2 imply mmx?

[saiarcot895, 2016/05/05 21:25:18]

It might (based on the options for the -march flag and the extensions it sets),
but it's not explicitly stated in the GCC documentation.

+    ]
+  }
+
   if (is_clang && is_debug) {
     # Allow comparing the address of references and 'this' against 0
     # in debug builds. Technically, these can never be null in