mpy-cross doesn't depend on any code in the extmod directory so completely
exclude it from the build (extmod may still be scanned for qstrs but that
is controlled by py/py.mk). This speeds up the build a little, and
improves abstraction of this component.
Also, make -I$(BUILD) take precedence over -I$(TOP) in case there are stray
files in the root directory that would be picked up.
fmode.c should only be included for builds targetting 'pure' windows, i.e.
msvc or mingw builds but not when using msys or cygwin's gcc (see #2298).
Just checking if the OS is windows and UNAME doesn't have msys stil leaves
the gate open for builds with cygwin's gcc since UNAME there is e.g.
CYGWIN_NT-6.1-WOW.
Fix this by checking for 'mingw' explicitly in the compiler version; both
gcc and clang have the -dumpmachine flag so the check should be ok for
all platforms.
The -ansi flag is used for C dialect selection and it is equivalent to -std=c90.
Because it goes right before -std=gnu99 it is ignored as for conflicting flags
GCC always uses the last one.
When compiling with msys2's gcc there's no need to apply the binary fmode
so adjust the Makefile to reflect that.
When compiling with mingw we need to include malloc.h since there is no
alloca.h, and the 64bit detection in mpconfigport.h needs some adjustment.
This is a fix for https://github.com/micropython/micropython/issues/2209:
by default a file created using open() uses text translation mode so writing
\n to it will result in the file having \r\n. This is obviously problematic
for binary .mpy files, so provide functions for setting the open mode
and use binary mode in mpy-cross' main().
Building in 32-bit mode was only to reduce binary size on 64-bit machines
and is otherwise not needed. Having it forced to 32-bit meant an
unnecessary dependency on 32-bit libraries that is now removed.
