[kernel] Expose a sysconf page to userspace

A structure, system_config, which is dynamically defined by the
definitions/sysconf.yaml config, is now mapped into every user address
space. The kernel fills this with information about itself and the
running machine.

User programs access this through the new j6_sysconf fake syscall in
libj6.

See: Github bug #242
See: [frobozz blog post](https://jsix.dev/posts/frobozz/)

Tags:

src/kernel/kernel.module

@@ -60,6 +60,8 @@ kernel = module("kernel",
         "syscalls/system.cpp",
         "syscalls/thread.cpp",
         "syscalls/vm_area.cpp",
+        "sysconf.cpp",
+        "sysconf.h.cog",
         "task.s",
         "tss.cpp",
         "vm_space.cpp",
@@ -69,9 +71,11 @@ from glob import glob
 from os.path import join
 
 layout = join(source_root, "definitions/memory_layout.yaml")
+sysconf = join(source_root, "definitions/sysconf.yaml")
 definitions = glob('definitions/**/*.def', recursive=True)
 
 kernel.add_depends(["memory.h.cog"], [layout])
+kernel.add_depends(["sysconf.h.cog"], [sysconf])
 kernel.add_depends(["syscall.cpp.cog", "syscall.h.cog", "syscalls.inc.cog"], definitions)
 
 kernel.variables['ldflags'] = ["${ldflags}", "-T", "${source_root}/src/kernel/kernel.ld"]