This commit introduces C++ support.

This commit introduces C++ support.

* configure.ac (OPT_CXXFLAGS): New variable.
(ARCH_CFLAGS): Renamed to ARCH_FLAGS.
(OS_FLAGS): New variable.
(CC_FLAGS, CXX_FLAGS): Likewise.
* m4/threads.m4 (ENABLE_THREADS): Set OS_FLAGS instead of ARCH_CFLAGS.
* src/cacao/Makefile.am (nodist_EXTRA_libjvm_la_SOURCES): Added to
force C++ linking.
* src/cacaoh/dummy.c (instruction_call_site): Added.
(icmd_table): Likewise.
(package_add): Renamed to Package_add.
[HAVE___THREAD] (thread_current): Added.
[!HAVE___THREAD) (thread_current_key): Likewise.
* src/cacaoh/headers.c (printmethod): Print _this instead of this, as
it's a C++ keyword.
* src/mm/boehm-gc/configure.ac: Don't use CACAO's CFLAGS anymore.
* src/mm/memory.h [__cplusplus]: Added define.
* src/native/jni.h [__cplusplus] (_Jv_JNIEnv): Likewise.
[__cplusplus] (_Jv_JavaVM): Likewise.
* src/native/vm/openjdk/jvm.c (vm/package.h): Removed.
(vm/package.hpp): Added.
(JVM_GetSystemPackage): Renamed package_find to Package_find.
* src/toolbox/list.h [__cplusplus]: Added define.
* src/vm/Makefile.am (libvm_la_SOURCES): Removed package.[ch], added
package.{cpp,hpp}.
* src/vm/vm.c (vm/package.h): Removed.
(vm/package.hpp): Added.
(vm_create): Renamed package_init to Package_initialize.
* src/vmcore/loader.c (vm/package.h): Removed.
(vm/package.hpp): Added.
(load_class_bootstrap): Renamed package_add to Package_add.
* src/vm/package.c,
src/vm/package.h: Moved from C...
* src/vm/package.cpp,
src/vm/package.hpp: ...to C++.