Makefile: fix parallel build failure

At the moment parallel build fails due to 2 causes:

1. parsetime.l tries to include incomplete y.tab.h, since y.tab.h is the result of yacc -d parsetime.y
2. when compiling y.tab.c, y.tab.c itself is not complete, since it is the result of yacc -d parsetime.y

So fix it by:

1. making parsetime.l to wait for y.tab.h to be created by yacc
2. waiting for y.tab.c and y.tab.h to be created before compile them

Signed-off-by: Giulio Benetti giulio.benetti@benettiengineering.com