[BUILD] Add build system module makefiles, add README how to use it.

mk/README

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+-------------------------------------------------------------------------------
+README
+-------------------------------------------------------------------------------
+
+  This directory contains makefile modular support files, that can be used in
+your project.
+
+  Each module is packaged with two inclusion makefiles, <module>-config.mk and
+<module>-rules.mk. The first one defines some new variables for the make, or
+appends values to the existing variables for the make. The second defines rules
+for support building.
+
+  So in your project, the <module>-config.mk should be included at some place,
+where you are defining variables (near the beginning of the file), and file
+<module>-rules.mk should be included in the rules part of makefile (somewhere
+near to the end of file).
+
+Example makefile using gcc compiler module:
+
+>>>>>>
+OBJS		+= foo.o bar.o
+
+CFLAGS		+= -O0 -g
+CPPFLAGS	+= -MD -MP $(@F).d
+CPPFLAGS	+= $(DEFS)
+CPPFLAGS	+= $(INCS)
+LDFLAGS		+= --static --nostartfiles
+LDLIBS		+= -Wl,--start-group -lc -lgcc -lnosys -Wl,--end-group
+# parameters for gcc module
+PREFIX		= arm-elf
+
+include $(OPENCM3_DIR)/mk/gcc-config.mk
+
+.PHONY: clean all
+
+all: binary.images
+
+%.images: %.elf %.hex
+
+include $(OPENCM3_DIR)/mk/gcc-rules.mk
+
+clean:
+	$(Q)$(RM) -rf binary.* *.o *.d
+
+-include $(OBJS:.o=.d)
+<<<<<<
+
+
+MODULES
+=======
+
+-------------------------------------------------------------------------------
+gcc
+-------------------------------------------------------------------------------
+
+  This module adds an extended support for GCC toolchain. This adds rules,
+neccessary for compiling C and C++ files into elf binary, and rules for
+generation of bin, hex, or srec output files for flashing.
+
+Variables to control the build process (should be set in your makefile):
+------------------------------------------------------------------------
+
+CFLAGS		C compiler flags
+CXXFLAGS	C++ compiler flags
+CPPFLAGS	C preprocessor flags (used for C and for C++ compiler)
+LDFLAGS		Linker flags
+ARCH_FLAGS	Architecture specification flags (-mcpu, -march etc )
+
+Variables to tell gcc about project dependencies and input files
+----------------------------------------------------------------
+
+LDSCRIPT	Linker script file name (can be generated or fixed)
+LIBDEPS		Array of library filenames that shoud be rebuilt if needed
+LDLIBS		Array of libraries to be linked with (array of -l<libname>)
+OBJS		Array of object files to be built

mk/gcc-config.mk

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+##
+## This file is part of the libopencm3 project.
+##
+## Copyright (C) 2014 Frantisek Burian <BuFran@seznam.cz>
+##
+## This library is free software: you can redistribute it and/or modify
+## it under the terms of the GNU Lesser General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## This library is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU Lesser General Public License for more details.
+##
+## You should have received a copy of the GNU Lesser General Public License
+## along with this library.  If not, see <http://www.gnu.org/licenses/>.
+##
+
+###############################################################################
+# The support makefile for GCC compiler toolchain, the rules part.
+#
+# please read mk/README for specification how to use this file in your project
+
+
+PREFIX		?= arm-none-eabi
+#PREFIX		?= arm-elf
+
+CC		:= $(PREFIX)-gcc
+CXX		:= $(PREFIX)-g++
+LD		:= $(PREFIX)-gcc
+AR		:= $(PREFIX)-ar
+AS		:= $(PREFIX)-as
+OBJCOPY		:= $(PREFIX)-objcopy
+OBJDUMP		:= $(PREFIX)-objdump
+GDB		:= $(PREFIX)-gdb
+SIZE		:= $(PREFIX)-size

mk/gcc-rules.mk

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+##
+## This file is part of the libopencm3 project.
+##
+## Copyright (C) 2014 Frantisek Burian <BuFran@seznam.cz>
+##
+## This library is free software: you can redistribute it and/or modify
+## it under the terms of the GNU Lesser General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## This library is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU Lesser General Public License for more details.
+##
+## You should have received a copy of the GNU Lesser General Public License
+## along with this library.  If not, see <http://www.gnu.org/licenses/>.
+##
+
+###############################################################################
+# The support makefile for GCC compiler toolchain, the rules part.
+#
+# please read mk/README for specification how to use this file in your project
+#
+
+%.bin: %.elf
+	@printf "  OBJCOPY $@\n"
+	$(Q)$(OBJCOPY) -Obinary $< $@
+
+%.hex: %.elf
+	@printf "  OBJCOPY $@\n"
+	$(Q)$(OBJCOPY) -Oihex $< $@
+
+%.srec: %.elf
+	@printf "  OBJCOPY $@\n"
+	$(Q)$(OBJCOPY) -Osrec $< $@
+
+%.list: %.elf
+	@printf "  OBJDUMP $@\n"
+	$(Q)$(OBJDUMP) -S $< > $@
+
+%.elf: $(OBJS) $(LDSCRIPT) $(LIBDEPS)
+	@printf "  LD      $(*).elf\n"
+	$(Q)$(LD) $(OBJS) $(LDLIBS) $(LDFLAGS) -T$(LDSCRIPT) $(ARCH_FLAGS)  -o $@
+
+%.o: %.c
+	@printf "  CC      $<\n"
+	$(Q)$(CC) $(CFLAGS) $(CPPFLAGS) $(ARCH_FLAGS) -o $@ -c $<
+
+%.o: %.cxx
+	@printf "  CXX     $<\n"
+	$(Q)$(CXX) $(CXXFLAGS) $(CPPFLAGS) $(ARCH_FLAGS) -o $@ -c $<
+
+%.o: %.cpp
+	@printf "  CXX     $(*).cpp\n"
+	$(Q)$(CXX) $(CXXFLAGS) $(CPPFLAGS) $(ARCH_FLAGS) -o $@ -c $<