[CMake] faking convenience libraries

[Brandon J. Van Every]

We need to compile the same underlying code 7 times for 7 different 
libraries.  3 of the resulting libs are dynamic and 4 are static.  We 
would use "convenience libraries" to do this, if it were portable and 
available in CMake.  We understand that "ar" in particular can't include 
static libraries in other static libraries.  How can we reduce the 
number of times we have to compile this code, without getting into a lot 
of hairy details?  Currently we do like the following:

####################################################################
#  PCRE LIBRARY                                                     #
####################################################################

# The PCRE code is used several times by the various Chicken libraries.  
It is tempting to create a
# PCRE library to be used by other Chicken libraries.  However, CMake 
doesn't support so-called
# "Convenience Libraries."  Static libraries can't include other static 
libraries as a component, at least
# not in a portable manner.  In particular, "ar" can't handle this.  So 
we take the path of least
# resistance and just explicitly include the source files in all the 
libraries we build.
#
# TODO: see if there's a way to reduce the number of times we must 
compile the PCRE code.

SET(PCRE_SOURCES
  chartables.c
  config.h
  pcre.h
  pcre_compile.c
  pcre_config.c
  pcre_dfa_exec.c
  pcre_exec.c
  pcre_fullinfo.c
  pcre_get.c
  pcre_globals.c
  pcre_internal.h
  pcre_maketables.c
  pcre_ord2utf8.c
  pcre_printint.c
  pcre_refcount.c
  pcre_study.c
  pcre_tables.c
  pcre_try_flipped.c
  pcre_ucp_findchar.c
  pcre_valid_utf8.c
  pcre_version.c
  pcre_xclass.c
)
ADD_PREFIX(${Chicken_SOURCE_DIR}/pcre/ PCRE_SOURCES)
SET(STATIC_FLAGS "${STATIC_FLAGS} -DPCRE_STATIC")

[...]

ADD_LIBRARY(libchicken SHARED ${CHICKEN_LIB_SOURCES} ${PCRE_SOURCES})

[and so forth]


Cheers,
Brandon Van Every