Move folly/PicoSpinLock.h to folly/synchronization/

Summary: [Folly] Move `folly/PicoSpinLock.h` to `folly/synchronization/`.

Differential Revision: D6830101

fbshipit-source-id: 529df14d9cda46bae5989f901ca73effbe0022e5

folly/Makefile.am

@@ -355,7 +355,6 @@ nobase_follyinclude_HEADERS = \
 	Overload.h \
 	PackedSyncPtr.h \
 	Padded.h \
-	PicoSpinLock.h \
 	Poly.h \
 	Poly-inl.h \
 	poly/Nullable.h \
@@ -439,6 +438,7 @@ nobase_follyinclude_HEADERS = \
 	synchronization/CallOnce.h \
 	synchronization/LifoSem.h \
 	synchronization/ParkingLot.h \
+	synchronization/PicoSpinLock.h \
 	synchronization/RWSpinLock.h \
 	synchronization/SaturatingSemaphore.h \
 	synchronization/SmallLocks.h \

folly/synchronization/SmallLocks.h

@@ -38,5 +38,5 @@
 
 #include <folly/Portability.h>
 #if FOLLY_X64 || FOLLY_AARCH64 || FOLLY_PPC64
-#include <folly/PicoSpinLock.h>
+#include <folly/synchronization/PicoSpinLock.h>
 #endif