Bug #55842 CMake: bad dependencies on sql/lex_hash.h

Fix by adding "DEPENDS gen_lex_hash" to ADD_CUSTOM_COMMAND(),
so it regenerates lex_hash.h whenever gen_lex_lash changes.

Also, make sql dependent on GenServerSource to avoid concurrent 
generation of lex_hash.h (once for sql , and in parallel for embedded)

sql/CMakeLists.txt

@@ -82,6 +82,7 @@ MYSQL_ADD_PLUGIN(partition ha_partition.cc STORAGE_ENGINE DEFAULT STATIC_ONLY
 RECOMPILE_FOR_EMBEDDED)
 
 ADD_LIBRARY(sql STATIC ${SQL_SOURCE})
+ADD_DEPENDENCIES(sql GenServerSource)
 DTRACE_INSTRUMENT(sql)
 TARGET_LINK_LIBRARIES(sql ${MYSQLD_STATIC_PLUGIN_LIBS} 
   mysys dbug strings vio regex   
@@ -188,6 +189,7 @@ ADD_EXECUTABLE(gen_lex_hash gen_lex_hash.cc)
 ADD_CUSTOM_COMMAND(
   OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/lex_hash.h
   COMMAND gen_lex_hash > lex_hash.h
+  DEPENDS gen_lex_hash
 )
 
 MYSQL_ADD_EXECUTABLE(mysql_tzinfo_to_sql tztime.cc)