Enabling setting MEM_HEAP_AREA_SIZE for linux host.

[ILyoan]

On linux host machine, CONFIG_MEM_HEAP_AREA_SIZE would be set 256KB by default. I cannot find the way to set the configuration from CMake build system.

I would be useful to set the heap size for host machine so that we can test with memory consumption problem on host without flashing binary into target device.

[egavrin]

It is possible to specify heap size in this file: https://github.com/Samsung/jerryscript/blob/master/jerry-core/config.h#L45

[ILyoan]

@egavrin Yes, sure we can. but I think it would be better to set heap limit as build parameter, without touching source file.

[akosthekiss]

The new build system now allows passing -DMEM_HEAP_SIZE_KB=... to cmake, which will define the CONFIG_MEM_HEAP_AREA_SIZE macro for the compiler.