core: unify handling of boot modules

Instead of solving the problem to deliver ROM modules to core while booting
differently for the several kernels (multi-boot, elfweaver, core re-linking),
this commit unifies the approaches. It always builds core as a library, and
after all binaries are built from a run-script, the run-tool will link an
ELF image out of the core-library and all boot modules. Thereby, core can
access its ROM modules directly.

This approach now works for all kernels except Linux.

With this solution, there is no [build_dir]/bin/core binary available anymore.
For debugging purposes you will find a core binary without boot modules, but
with debug symbols under [run_dir].core.

Fix #2095

repos/base-linux/mk/spec/linux.mk

@@ -12,6 +12,7 @@ LD_TEXT_ADDR     ?= 0x01000000
 LD_SCRIPT_STATIC  = $(call select_from_repositories,src/ld/genode.ld) \
                     $(call select_from_repositories,src/ld/stack_area.nostdlib.ld)
 else
+LD_TEXT_ADDR     ?=
 LD_SCRIPT_STATIC ?=
 endif