Add minimal-system-image-x86_64

This element produces a disk image that boots in QEMU. It has a kernel,
BusyBox, and little else; but should be suitable as a basis for more
grand endeavours.

This disk image we produce is 53MB. I spent a while trying to get this
as small as possible and this is as far as I got:

  * The boot partition seems to have a minimum size just over 32MB;
    lower than that and SYSLINUX fails to write the boot sector. The
    combined size of the initramfs and kernel is about 32MB, so I
    imagine that's what limits us.

  * The main partition is limited in size only by the amount of binaries
    that we put there.

  * We have a useless 40KB swap partition, which the x86image plugin
    insists on creating for us. Again 40KB is the minimum size that
    `mkswap` will allow. It's possible to override or modify the
    x86image plugin to avoid swap altogether but I'm not sure of the
    best way to proceed.

There are a few dependency cleanups in the bsp-generic stack; previously
we'd build the whole 'foundation' stack which took ages and wasn't
needed at all.

1 files changed, 12 insertions, 0 deletions

diff --git a/elements/systems/minimal-system.bst b/elements/systems/minimal-system.bst
new file mode 100644
index 00000000..57a5698a
--- /dev/null
+++ b/elements/systems/minimal-system.bst
@@ -0,0 +1,12 @@
+kind: compose
+description: Minimal system
+
+depends:
+- filename: systems/minimal-system-content.bst
+  type: build
+- filename: initramfs/initramfs-gz.bst
+  type: build
+
+config:
+  include:
+  - runtime