C++ support for RT-Thread

This is the C++ component in RT-Thread RTOS. In order to support C++ language, this component implement a basic environment, such as new/delete operators.

Because RT-Thread RTOS is used in embedded system mostly, there are some rules for C++ applications:

1. DOES NOT use exception.
2. DOES NOT use Run-Time Type Information (RTTI).
3. Template is discouraged and it easily causes code text large.
4. Static class variables are discouraged. The time and place to call their constructor function could not be precisely controlled and make multi-threaded programming a nightmare.
5. Multiple inheritance is strongly discouraged, as it can cause intolerable confusion.

NOTE: The libc (RT_USING_LIBC in rtconfig.h) must be enable.

About GNU GCC compiler

please add following string in your ld link script:

// in your .text section
PROVIDE(__ctors_start__ = .);
/* old GCC version uses .ctors */
KEEP(*(SORT(.ctors.*)))
KEEP(*(.ctors))
/* new GCC version uses .init_array */
KEEP (*(SORT(.init_array.*)))
KEEP (*(.init_array))
PROVIDE(__ctors_end__ = .);

. = ALIGN(4);

// as a standalone section if you use ARM target.

/* The .ARM.exidx section is used for C++ exception handling. */
/* .ARM.exidx is sorted, so has to go in its own output section.  */
__exidx_start = .;
ARM.exidx :
{
    *(.ARM.exidx* .gnu.linkonce.armexidx.*)

    /* This is used by the startup in order to initialize the .data secion */
    _sidata = .;
} > CODE
__exidx_end = .;

/* .data section which is used for initialized data */

// in your .data section
PROVIDE(__dtors_start__ = .);
KEEP(*(SORT(.dtors.*)))
KEEP(*(.dtors))
PROVIDE(__dtors_end__ = .);

. = ALIGN(4);