U-boot itself generally builds with -nostdinc.  This is because the
bootloader needs to be completely standalone.  In the sandbox arch
though, we need a little bit of code to glue the u-boot world to the
host operating system, and we need to be able to access the host
libc's headers in order to do so.

Currently, we're using -I/usr/include to workaround the global
-nostdinc, but that doesn't work for everyone and for all headers.
Instead, let's filter out -nostdinc when building the os.c code.

Without this patch, some distros hit errors such as:
---8<---
In file included from /usr/include/fcntl.h:27:0,
                 from os.c:22:
/usr/include/features.h:323:26: fatal error:
     bits/predefs.h: No such file or directory
--->8---

Signed-off-by: Andreas Bießmann <biessmann@corscience.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Making sleep command work

Signed-off-by: Matthias Weisser <weisserm@arcor.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Using mmap to allocate memory from the OS for RAM simulation we can use
u-boot own malloc implementation.

Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Matthias Weisser <weisserm@arcor.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Simon Glass <sjg@chromium.org>

This allows us to act like a serial device: we get tab chars and CTRL+C
and respond appropriately.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Tested-by: Simon Glass <sjg@chromium.org>

Add a main program so that we can run U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>

We want to keep all OS-dependent code in once place, with a simple interface
to U-Boot. For now, this is that place.

Signed-off-by: Simon Glass <sjg@chromium.org>

This is an initial implementation with all functions defined but not working.

The lds file is very simple since we can mostly rely on the linker defaults.

Signed-off-by: Simon Glass <sjg@chromium.org>