Fix performance regressions due to lazy initialization.

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index 08f4495b53b389cf95de81d74c0f1e582d20ff5d..cb4adaa90b5739a0bd5ba615fc4a0864eda7398c 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -105,6 +105,15 @@ void OS::SetUp() {
 }
 
 
+void MathSetup();  // Defined in platform-posix.cc.
+
+void OS::PostSetUp() {
+  // Math functions depend on CPU features therefore they are initialized after
+  // CPU.
+  MathSetup();
+}
+
+
 uint64_t OS::CpuFeaturesImpliedByPlatform() {
   return 0;  // Linux runs on anything.
 }