[Common] introduce a CACHE_LINE_SIZE define

This define will be used in future patches.

emper/Common.hpp

@@ -30,9 +30,10 @@ using func_t = std::function<void()>;
 #define likely(x) __builtin_expect(!!(x), 1)
 #define unlikely(x) __builtin_expect(!!(x), 0)
 
-#define ALIGN_TO_CACHE_LINE alignas(64)
+#define CACHE_LINE_SIZE 64
+#define ALIGN_TO_CACHE_LINE alignas(CACHE_LINE_SIZE)
 #define CACHE_LINE_EXCLUSIVE(T, symbol)                                          \
-	std::aligned_storage<64, 64>::type __##symbol##_mem; \
+	std::aligned_storage<CACHE_LINE_SIZE, CACHE_LINE_SIZE>::type __##symbol##_mem; \
 	T& symbol = *new (&__##symbol##_mem) T()
 
 [[noreturn]] void die(const char* message, bool usePerror);