Subzero: Fix a build error.  Also reformat.

BUG= none
TBR=nicolascapens@chromium.org

Review URL: https://codereview.chromium.org/2328873003 .
diff --git a/src/IceMemory.cpp b/src/IceMemory.cpp
index 0026661..ce1ff6a 100644
--- a/src/IceMemory.cpp
+++ b/src/IceMemory.cpp
@@ -38,7 +38,7 @@
   ICE_TLS_SET_FIELD(CfgAllocator, Allocator);
 }
 
-void CfgAllocatorTraits::set_current(nullptr_t) {
+void CfgAllocatorTraits::set_current(std::nullptr_t) {
   ICE_TLS_SET_FIELD(CfgAllocator, nullptr);
 }