BuildSystem: Rewrite port compilation system

Now ports define some environment variables, and call a unified bash
script that handles configuration, recompilation and installation.

If a port uses non-configure buildsystem, port script can also specify
custom build and install step.

ports/doom/patches/0001-Add-support-for-banan-os.patch

@@ -29,16 +29,16 @@ index 0000000..0878148
 +	VB=@
 +endif
 +
-+CC=$(BANAN_TOOLCHAIN_PREFIX)/bin/$(BANAN_ARCH)-banan_os-gcc
-+CXX=$(BANAN_TOOLCHAIN_PREFIX)/bin/$(BANAN_ARCH)-banan_os-g++
++CC=$(BANAN_ARCH)-banan_os-gcc
++CXX=$(BANAN_ARCH)-banan_os-g++
 +CFLAGS+=-O3 -Wall -DNORMALUNIX -DLINUX -DSNDSERV -D_DEFAULT_SOURCE
 +CXXFLAGS+=$(CFLAGS) --std=c++20
 +LDFLAGS+=
 +LIBS+=-lgui -linput -lstdc++
 +
 +# subdirectory for objects
-+OBJDIR=build-$(BANAN_ARCH)
-+OUTPUT=$(OBJDIR)/doomgeneric
++OBJDIR=build
++OUTPUT=$(OBJDIR)/doom
 +
 +SRC_DOOM = dummy.o am_map.o doomdef.o doomstat.o dstrings.o d_event.o d_items.o d_iwad.o d_loop.o d_main.o d_mode.o d_net.o f_finale.o f_wipe.o g_game.o hu_lib.o hu_stuff.o info.o i_cdmus.o i_endoom.o i_joystick.o i_scale.o i_sound.o i_system.o i_timer.o memio.o m_argv.o m_bbox.o m_cheat.o m_config.o m_controls.o m_fixed.o m_menu.o m_misc.o m_random.o p_ceilng.o p_doors.o p_enemy.o p_floor.o p_inter.o p_lights.o p_map.o p_maputl.o p_mobj.o p_plats.o p_pspr.o p_saveg.o p_setup.o p_sight.o p_spec.o p_switch.o p_telept.o p_tick.o p_user.o r_bsp.o r_data.o r_draw.o r_main.o r_plane.o r_segs.o r_sky.o r_things.o sha1.o sounds.o statdump.o st_lib.o st_stuff.o s_sound.o tables.o v_video.o wi_stuff.o w_checksum.o w_file.o w_main.o w_wad.o z_zone.o w_file_stdc.o i_input.o i_video.o doomgeneric.o doomgeneric_banan_os.o
 +OBJS += $(addprefix $(OBJDIR)/, $(SRC_DOOM))