Add build step in applications for linked static libraries due to their prl information add add them as PRE_TARGETDEP

Building a complex project source tree is quite simple and "cmake" like possible with the SUBDIRS directive. Works if i e.g. build on top dir and all libs and depending projects are build

But now i want to build a single app in the project tree (first checkout)
1) qmake on top of the project tree
2) cd into subdirectory of this program and run make

Expected behaviour: all dependent libs are build and linked
Real behaviour: build fails due to libraries are not build, but all information is available:

• prl contains lib name
• prl contains build dir
• prl contains config flags.

Suggestion: just add to the prl a "how is the lib build" line.
Automatically create build instructions from the prls of the lib i link against.

So the application does know how to build the libs if not present. no complete build instruction necessary,
just a simple
cd to lib dir and make

The prl of the libs are found correctly and added to the makefile as dependency