[SYCL][NFC] Add missing unordered_map include (#7880)

This fixes build on MacOS.

Author: AlexeySachkov

llvm/lib/SYCLLowerIR/ESIMD/LowerESIMDSlmReservation.cpp

@@ -68,6 +68,8 @@
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Module.h"
 
+#include <unordered_map>
+
 #define DEBUG_TYPE "LowerESIMDSlmAllocPass"
 
 namespace llvm {