fix compiling item counts by not including MKDIRs in the item list

'make' ends at [315/318], but the build was successful.
The problem was that 'mkdir -p' sometimes creates multiple targets at once, that makes the difference of item counts between dry run and actual build. (such as MKDIR build/blah/, then MKDIR build/, the latter is ignored in actual building)
Alternative solution to this could be making mkdir parent directory a dependency, but it looks pretty painful to me.