Add support for loongarch

cmake/FindArch.cmake

     #else
         #error cmake_ARCH ppc
     #endif
+#elif defined(__loongarch__) || defined(__loongarch64)
+    #error cmake_ARCH loongarch64
 #endif
 
 #error cmake_ARCH unknown

contrib/backward-cpp/backward.hpp

     #else
       error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.pc);
     #endif
+#elif defined(__loongarch__)
+    error_addr = reinterpret_cast<void *>(uctx->uc_mcontext.__pc);
 #elif defined(__mips__)
     error_addr = reinterpret_cast<void *>(
         reinterpret_cast<struct sigcontext *>(&uctx->uc_mcontext)->sc_pc);

contrib/libev/ev.c

       #define ECB_MEMORY_FENCE         __asm__ __volatile__ ("tb1 0,%%r0,128" : : : "memory")
     #elif defined __sh__
       #define ECB_MEMORY_FENCE         __asm__ __volatile__ (""         : : : "memory")
+    #elif defined __loongarch__ || __loongarch64
+      #define ECB_MEMORY_FENCE         __asm__ __volatile__ ("dbar %0 ": : "I"(0) : "memory")
     #endif
   #endif
 #endif

src/rspamd.c

 	return "ARM64";
 #elif defined(__arm__) || defined(_M_ARM)
 	return "ARM";
+#elif defined(__loongarch__) || defined(__loongarch64)
+	return "LOONGARCH64";
 #elif defined(__mips__)
 	return "MIPS";
 #elif defined(__powerpc__) || defined(_M_PPC)