compiler: Strip .image_header section in bin

This sepcifies .image_header section that will be removed from elf when .bin file is generated.

So far there is no such section used.
With this change it is possible to have elf file that already contains image header (in .image_header section).
This header will be removed and so create image will add new one.

Elf file containing image header can be flashed by debugger, this way output build from cmake can be use directly by IDE that supports cmake.

newt/toolchain/compiler.go

@@ -1108,6 +1108,8 @@ func (c *Compiler) generateExtras(elfFilename string,
  ".bss.core",
  "-R",
  ".bss.core.nz",
+ "-R",
+ ".image_header",
  "-O",
  "binary",
  elfFilename,