This is a set of headers and CRT files sufficient to do development for the
original AT&T UNIX System V/386 Release 4.0. I do not have the original C
compiler for this system, and gave up on finding it. Instead, I used headers
from the earliest public release of OpenSolaris, and cobbled the crt files by
extracting them from an actual binary. The include files contain WAY more than
is necessary, and interfaces for many unsupported APIs. I'm removing things
only when they break builds, for simplicity sake.

The header files are licensed under the CDDL.

To use this, it must be extracted to a cross compiler prefix. For instance, if
you intend to build your cross compiler in /opt/cross/i386-sysv4, then this
belongs in /opt/cross/i386-sysv4/i386-sysv4 .

To build a complete cross compiler:

1) Put this repo in the right path.

2) Put the original libc in the right place:
    cp .../lib/ /opt/cross/i386-sysv4/i386-sysv4/lib
    ln -s /opt/cross/i386-sysv4/i386-sysv4/lib/

3) Build and install binutils. Suggested configure:
    ../configure --prefix /opt/cross/i386-sysv4 --target=i386-sysv4

4) Compile the crt files:
    cd /opt/cross/i386-sysv4/i386-sysv4/lib
    for crt in *.s; do i386-sysv4-as $crt -o ${crt/.s}.o; done

5) Build and install GCC. Note that the latest version of GCC with support for
   SVR4 is 4.3.6; later versions would probably work with the i386-elf target,
   but this is untested. Suggested configure:
    ../configure --prefix /opt/cross/i386-sysv4 --target=i386-sysv4 \
        --enable-obsolete --enable-languages=c --disable-threads \
        --disable-libssp --disable-libgomp

6) Remove the broken "fixed" headers:
    rm -rf /opt/cross/i386-sysv4/lib/gcc/i386-sysv4/4.3.6/include-fixed