MDEV-11611 fix Ninja build

ninja doesn't like when a dummy target name matches a generated file name

dbug/CMakeLists.txt

@@ -58,13 +58,13 @@ IF(NOT WIN32 AND NOT CMAKE_GENERATOR MATCHES Xcode)
     ADD_CUSTOM_COMMAND(OUTPUT user.ps
                        DEPENDS user.r ${OUTPUT_INC} ${SOURCE_INC}
                        COMMAND ${GROFF} -mm ${CMAKE_CURRENT_SOURCE_DIR}/user.r > user.ps || touch user.ps)
-    ADD_CUSTOM_TARGET(user.ps ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/user.ps)
+    ADD_CUSTOM_TARGET(user_ps ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/user.ps)
   ENDIF(GROFF)
   IF(NROFF)
     ADD_CUSTOM_COMMAND(OUTPUT user.t
                        DEPENDS user.r ${OUTPUT_INC} ${SOURCE_INC}
                        COMMAND ${NROFF} -mm ${CMAKE_CURRENT_SOURCE_DIR}/user.r > user.t || touch user.t)
-    ADD_CUSTOM_TARGET(user.t ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/user.t)
+    ADD_CUSTOM_TARGET(user_t ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/user.t)
   ENDIF(NROFF)
 
 ENDIF()