base: restructure signal-submit initialization

This patch allows core's 'Signal_transmitter' implementation to sidestep
the 'Env::Pd' interface and thereby adhere to a stricter layering within
core. The 'Signal_transmitter' now uses - on kernels that depend on it -
a dedicated (and fairly freestanding) RPC proxy mechanism for signal
deliver, instead of channeling signals through the 'Pd_session::submit'
RPC function.

repos/base-linux/lib/mk/base-linux-common.mk

@@ -9,7 +9,6 @@ include $(BASE_DIR)/lib/mk/base-common.inc
 LIBS += syscall-linux
 
 SRC_CC += region_map_mmap.cc debug.cc
-SRC_CC += signal_submit.cc
 SRC_CC += rpc_dispatch_loop.cc
 SRC_CC += thread_env.cc
 SRC_CC += capability.cc

repos/base-linux/lib/mk/base-linux.mk

@@ -6,7 +6,8 @@
 
 include $(REP_DIR)/lib/mk/base-linux.inc
 
-LIBS   += startup-linux base-linux-common timeout
+LIBS   += startup-linux base-linux-common cxx timeout
 SRC_CC += thread.cc thread_myself.cc thread_linux.cc
 SRC_CC += capability_space.cc capability_raw.cc
 SRC_CC += attach_stack_area.cc
+SRC_CC += signal_transmitter.cc signal.cc

repos/base-linux/lib/mk/lx_hybrid.mk

@@ -1,4 +1,5 @@
 SRC_CC += lx_hybrid.cc new_delete.cc capability_space.cc
+SRC_CC += signal_transmitter.cc signal.cc
 
 vpath new_delete.cc $(BASE_DIR)/src/lib/cxx
 vpath lx_hybrid.cc   $(REP_DIR)/src/lib/lx_hybrid

repos/base-linux/src/core/linux/target.mk

@@ -24,6 +24,8 @@ SRC_CC        = main.cc \
                 core_rpc_cap_alloc.cc \
                 io_mem_session_component.cc \
                 signal_source_component.cc \
+                signal_transmitter_proxy.cc \
+                signal_receiver.cc \
                 trace_session_component.cc \
                 thread_linux.cc \
                 stack_area.cc \
@@ -54,6 +56,8 @@ vpath capability_space.cc         $(GEN_CORE_DIR)
 vpath rpc_cap_factory_l4.cc       $(GEN_CORE_DIR)
 vpath platform_services.cc        $(GEN_CORE_DIR)
 vpath signal_source_component.cc  $(GEN_CORE_DIR)
+vpath signal_transmitter_proxy.cc $(GEN_CORE_DIR)
+vpath signal_receiver.cc          $(GEN_CORE_DIR)
 vpath trace_session_component.cc  $(GEN_CORE_DIR)
 vpath core_rpc_cap_alloc.cc       $(GEN_CORE_DIR)
 vpath default_log.cc              $(GEN_CORE_DIR)