[CMake] Convert libtool convenience libraries to cmake

[Yevgen Muntyan]

Hi,

I want to convert an autotools project to cmake. But, I don't know how 
to solve the problem of the
convenience libraries. The issue is: the project builds a shared library 
of bunch of libtool convenience
libraries. Each convenience library uses different compilation flags 
(which is very important). So I can't
simply take all sources I got and stuff them into a shared library with 
add_library(). Could someone
please advise on what to do here? I really really want to convert this 
to cmake because I need a win32
visual studio build and I don't want to cope with two build systems.

The project is roughly as follows:

top/
  subdir1/
    file1.c
    file2.c
  subdir2/
    file3.c
    file4.c

file1.c and file2.c get compiled with SUB1_CFLAGS into libsub1.la,
file3.c and file4.c get compiled with SUB2_CFLAGS into libsub2.la,
libsub1.la and libsub2.la link into libfoolala.so/dll.
(Those files must be compiled with different flags, I can't trade that off)

Thanks!
Yevgen