CMakeLists.txt: add BUILDCPP option

C++ is a mandatory dependency since version 1.4.0 and
122cab1f1e

As a result, build on embedded toolchains that do not support C++ fails
on:

CMake Error at CMakeLists.txt:2 (project):
  The CMAKE_CXX_COMPILER:

    /home/naourr/work/instance-1/output-1/per-package/mraa/host/bin/arm-linux-g++

  is not a full path to an existing compiler tool.

Fixes:
 - http://autobuild.buildroot.org/results/31086422e03611c16ab59c4418e3669b580bc0c0

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required (VERSION 2.8.11)
-project (mraa C CXX)
+project (mraa C)
 
 FIND_PACKAGE (Threads REQUIRED)
 
@@ -11,6 +11,8 @@ else ()
   set (CMAKE_C_STANDARD 99)
 endif ()
 
+option (BUILDCPP "Enable C++ (needed by FTDI4222 and tests)" ON)
+
 ###############################################################################
 # Detect supported warning flags
 # Modified from work By Dan Liew (fpbench - MIT)
@@ -33,6 +35,8 @@ set (MRAA_C_WARNING_FLAGS
   -Werror=missing-parameter-type
 )
 
+include (CheckCCompilerFlag)
+if (BUILDCPP)
   # Warning flags for the C++ compiler only
   set (MRAA_CXX_WARNING_FLAGS
     -Wnon-virtual-dtor
@@ -40,8 +44,9 @@ set (MRAA_CXX_WARNING_FLAGS
     -Wreorder
   )
 
-include (CheckCCompilerFlag)
+  enable_language (CXX)
   include (CheckCXXCompilerFlag)
+endif ()
 function (MRAA_SANITIZE_FLAG_NAME OUTPUT_VAR FLAG)
   string (REPLACE "-" "_" SANITIZED_FLAG_NAME "${FLAG}")
   string (REPLACE "/" "_" SANITIZED_FLAG_NAME "${SANITIZED_FLAG_NAME}")
@@ -62,6 +67,7 @@ foreach (flag ${MRAA_BOTH_WARNING_FLAGS} ${MRAA_C_WARNING_FLAGS})
   endif ()
 endforeach ()
 
+if (BUILDCPP)
   # Globally set C++ compiler warning flags that are supported and emit
   # a warning about unsupported flags
   foreach (flag ${MRAA_BOTH_WARNING_FLAGS} ${MRAA_CXX_WARNING_FLAGS})
@@ -84,6 +90,7 @@ function(use_cxx_11 targetname)
       message(FATAL_ERROR "Target '${targetname}' requires c++11 which is not supported by this compiler")
     endif()
   endfunction()
+endif()
 
 # Set CMAKE_INSTALL_LIBDIR if not defined
 include(GNUInstallDirs)

src/java/CMakeLists.txt

@@ -16,7 +16,9 @@ include_directories (
 set_source_files_properties (mraajava.i PROPERTIES SWIG_FLAGS ";-package;mraa;-I${CMAKE_BINARY_DIR}/src")
 set_source_files_properties (mraajava.i PROPERTIES CPLUSPLUS ON)
 
+if (BUILDCPP)
   set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive -DJAVACALLBACK")
+endif()
 set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DJAVACALLBACK")
 
 if (NOT DEFINED ENV{JAVA_HOME_NATIVE})

src/javascript/CMakeLists.txt

@@ -36,6 +36,7 @@ set_target_properties (mraajs PROPERTIES
 )
 
 message (STATUS "INFO - swig Version ${SWIG_VERSION}")
+if (BUILDCPP)
   message (STATUS "INFO - CXX compiler Version ${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}")
 
   if (${V8_VERSION_MAJOR} GREATER 3)
@@ -57,6 +58,7 @@ if (${V8_VERSION_MAJOR} GREATER 3)
       set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${MRAA_CXX11_WORKAROUND_OPTION} ")
     endif ()
   endif ()
+endif ()
 
 # If a CMAKE_INSTALL_PREFIX has NOT been provided, set NODE_MODULE_INSTALL_PATH
 # base on the NODE_ROOT_DIR.