Fix builds when using CMake < v3.15

CMake before version 3.15 does not support creating an ALIAS library for
a library of UNKNOWN type via its command add_library().
Due to other fixes we can now skip the alias step when importing an
already installed hiredis library and use correct name directly.

CMakeLists.txt

@@ -127,9 +127,9 @@ if(NOT hiredis_FOUND)
   message("CMake package for 'hiredis' not found, searching for the library..")
   find_library(HIREDIS_LIB hiredis REQUIRED)
   find_path(HIREDIS_INCLUDES hiredis/hiredis.h)
-  add_library(hiredis UNKNOWN IMPORTED GLOBAL)
-  set_target_properties(hiredis PROPERTIES IMPORTED_LOCATION ${HIREDIS_LIB})
-  set_target_properties(hiredis PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${HIREDIS_INCLUDES})
+  add_library(hiredis::hiredis UNKNOWN IMPORTED GLOBAL)
+  set_target_properties(hiredis::hiredis PROPERTIES IMPORTED_LOCATION ${HIREDIS_LIB})
+  set_target_properties(hiredis::hiredis PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${HIREDIS_INCLUDES})
 endif()
 
 if(NOT TARGET hiredis::hiredis)
@@ -154,9 +154,9 @@ if(ENABLE_SSL)
     message("CMake package for 'hiredis_ssl' not found, searching for the library..")
     find_library(HIREDIS_SSL_LIB hiredis_ssl REQUIRED)
     find_path(HIREDIS_SSL_INCLUDES hiredis/hiredis_ssl.h)
-    add_library(hiredis_ssl UNKNOWN IMPORTED GLOBAL)
-    set_target_properties(hiredis_ssl PROPERTIES IMPORTED_LOCATION ${HIREDIS_SSL_LIB})
-    set_target_properties(hiredis_ssl PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${HIREDIS_SSL_INCLUDES})
+    add_library(hiredis::hiredis_ssl UNKNOWN IMPORTED GLOBAL)
+    set_target_properties(hiredis::hiredis_ssl PROPERTIES IMPORTED_LOCATION ${HIREDIS_SSL_LIB})
+    set_target_properties(hiredis::hiredis_ssl PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${HIREDIS_SSL_INCLUDES})
   endif()
 
   if(NOT TARGET hiredis::hiredis_ssl)