Add CMake building system support about jansson

[akheron]

Hi, and thanks for the suggestion. However, I'm not willing to support two different build systems. Autotools works fine for me (and for others), and if it cannot be used for some reason, it's quite straightforward just to take all .c files and compile them as a library by hand.

[quarnster]

For anyone else wanting CMake support, here's the CMakeLists.txt I wrote which properly configures jansson_config.h and sets up a install target:

cmake_minimum_required(VERSION 2.8)

include(CheckSymbolExists)
include(CheckCSourceCompiles)
check_symbol_exists(localeconv locale.h json_have_localeconv)
if(NOT json_have_localeconv)
    set(json_have_localeconv 0)
endif()
check_c_source_compiles("int main() { long long test = 0; return test; }" json_have_long_long)
if(NOT json_have_long_long)
    set(json_have_long_long 0)
endif()
check_c_source_compiles("inline int test() { return 0; }\nint main() { return test(); }" json_inline)
if(json_inline)
    set(json_inline inline)
endif()
configure_file(${CMAKE_CURRENT_SOURCE_DIR}/src/jansson_config.h.in ${CMAKE_CURRENT_BINARY_DIR}/jansson_config.h)
set(json_have_long_long 0)
include_directories(${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/src)
add_library(jansson STATIC
    src/dump.c
    src/error.c
    src/hashtable.c
    src/load.c
    src/memory.c
    src/pack_unpack.c
    src/strbuffer.c
    src/strconv.c
    src/utf.c
    src/value.c)


install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/src/jansson.h ${CMAKE_CURRENT_BINARY_DIR}/jansson_config.h DESTINATION include)
install(TARGETS jansson ARCHIVE DESTINATION lib)