build: Do as much as possible inside of the SDK container.

Parts of the rules, including the magical ones created via
make/rules-*.mk, are executed inside of the container via SHELL
override, and parts are executed on the host side.

This makes reasoning about and debugging the rules much harder than it
should be. It also requirs the users to have certain programs installed
on the host in addition to docker/podman.

With this change `make` will act as a simple pass through to inside of
the container for the most part.

One notable exception is installation which still happens the host side.

make/rules-source.mk

@@ -15,7 +15,6 @@
 define create-rules-source
 $(2)_SRC = $$(OBJ)/src-$(1)
 
-ifeq ($(CONTAINER),)
 $(1)-rebuild:
 .PHONY: $(1)-rebuild
 
@@ -29,7 +28,6 @@ $$(OBJ)/.$(1)-source: $$(shell echo -n 'syncing $(1)... ' >&2 && \
 	touch $$@
 
 $$(OBJ)/.$(1)-post-source: $$(OBJ)/.$(1)-source
-container-build: $$(OBJ)/.$(1)-post-source
 
 $(1)-source: $$(OBJ)/.$(1)-post-source
 .PHONY: $(1)-source
@@ -47,7 +45,6 @@ $(1)-distclean::
 clean: $(1)-clean
 distclean: $(1)-distclean
 .PHONY: clean distclean
-endif
 endef
 
 rules-source = $(call create-rules-source,$(1),$(call toupper,$(1)),$(2))