This commit adds a new tool called mpy_ld.py which is essentially a linker
that builds .mpy files directly from .o files. A new header file
(dynruntime.h) and makefile fragment (dynruntime.mk) are also included
which allow building .mpy files from C source code. Such .mpy files can
then be dynamically imported as though they were a normal Python module,
even though they are implemented in C.
Converting .o files directly (rather than pre-linked .elf files) allows the
resulting .mpy to be more efficient because it has more control over the
relocations; for example it can skip PLT indirection. Doing it this way
also allows supporting more architectures, such as Xtensa which has
specific needs for position-independent code and the GOT.
The tool supports targets of x86, x86-64, ARM Thumb and Xtensa (windowed
and non-windowed). BSS, text and rodata sections are supported, with
relocations to all internal sections and symbols, as well as relocations to
some external symbols (defined by dynruntime.h), and linking of qstrs.
Damien George