[build] Move configs/ to assets/build/

I was sick of `configs` colliding with `configure`, and these are
(mostly) static asset files anyway, they should live under assets/.

assets/build/kernel-debug.yaml

@@ -0,0 +1,59 @@
+---
+extends: base
+
+variables:
+  asflags: [ "-I${source_root}/src/kernel/" ]
+
+  ccflags: [
+    "--target=x86_64-jsix-elf",
+    "-fno-stack-protector",
+
+    "-I${source_root}/external",
+
+    "-nostdinc",
+    "-nostdlib",
+    "-ffreestanding",
+    "-nodefaultlibs",
+    "-fno-builtin",
+    "-fno-plt",
+
+    "-mno-sse",
+    "-fno-omit-frame-pointer",
+    "-mno-red-zone",
+    "-mcmodel=kernel",
+    "-fvisibility=hidden",
+    "-fvisibility-inlines-hidden",
+
+    "-g3",
+    "-ggdb",
+
+    "-D__ELF__",
+    "-D__jsix__",
+    "-D__j6kernel",
+    "-U__linux",
+    "-U__linux__",
+    "-DPRINTF_ALIAS_STANDARD_FUNCTION_NAMES=1",
+    "-DPRINTF_INCLUDE_CONFIG_H=1",
+
+    "-isystem${build_root}/include/libc",
+    "-isystem${source_root}/sysroot/include",
+    "--sysroot='${source_root}/sysroot'" ]
+
+
+  cflags: [ '-nostdinc' ]
+
+  cxxflags: [
+    "-fno-exceptions",
+    "-fno-rtti",
+    "-nostdinc",
+    "-isystem${source_root}/sysroot/include/c++/v1" ]
+
+  ldflags: [
+    "-g",
+    "-m", "elf_x86_64",
+    "-nostdlib",
+    "-Bstatic",
+    "--no-eh-frame-hdr",
+    "-z", "norelro",
+    "-z", "separate-code" ]
+