Move immintrin/arm_neon includes to where they are used.

src/core/SkSharedMutex.h

Index: src/core/SkSharedMutex.h
diff --git a/src/core/SkSharedMutex.h b/src/core/SkSharedMutex.h
index 21c9f46d64058f28e4d1273d5b40095340a8a4dd..302940bbc402cf84002f8c740b395a3ff0b347c9 100644
--- a/src/core/SkSharedMutex.h
+++ b/src/core/SkSharedMutex.h
@@ -14,6 +14,18 @@
 
 #ifdef SK_DEBUG
     #include "SkMutex.h"
+
+    // On GCC 4.8, targeting ARMv7 with NEON, using libc++, we need to typedef float float32_t,
+    // (or include <arm_neon.h> which does that) before #including <memory> here.
+    // This makes no sense.  I'm not very interested in understanding why... this is an old,
+    // bizarre platform configuration that we should just let die.
+    #include <ciso646>  // Include something innocuous to define _LIBCPP_VERISON if it's libc++.
+    #if defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ == 8 \
+     && defined(SK_CPU_ARM32) && defined(SK_ARM_HAS_NEON) \
+     && defined(_LIBCPP_VERSION)
+        typedef float float32_t;
+    #endif
+
     #include <memory>
 #endif  // SK_DEBUG