[CMake] Always compile source file in debug

[Belcourt, Kenneth]

Hi,

Apologies if this has been answered before.  In an effort to ensure  
cross-platform consistent results, I need to force some (C++ and  
Fortran) source files to always be built debug.  Is there any easy  
syntax to do this?

I build our libraries like this.

SET(SRCS
   ${EXEC_DIR}/AfterStep.f90
   ${EXEC_DIR}/ArgCF_Connect.f90
   ${EXEC_DIR}/ArgCF_Solve.f90
   ...
)

ADD_LIBRARY(exec ${SRCS})

-- Noel