[build] Move init to its own target

In order to allow -fpic and -fpie in the user target, move init to it's
own target -- it needs its own special build rules to make it loadable
by boot.

assets/build/target.init.yaml

@@ -0,0 +1,34 @@
+---
+ccflags: [
+  "--target=x86_64-jsix-elf",
+  "-fno-omit-frame-pointer",
+  "-fno-stack-protector",
+
+  "-fvisibility=hidden",
+  "-fvisibility-inlines-hidden",
+
+  "-D__ELF__",
+  "-D__jsix__",
+  "-U__linux",
+  "-U__linux__",
+
+  "--sysroot='${source_root}/sysroot'"
+]
+
+
+cxxflags: [
+  "-fno-exceptions",
+  "-fno-rtti",
+]
+
+ldflags: [
+  "-Bstatic",
+  "-m", "elf_x86_64",
+  "--sysroot='${source_root}/sysroot'",
+  "--no-eh-frame-hdr",
+  "-L", "${source_root}/sysroot/lib",
+  "-z", "separate-code",
+  "-lc++", "-lc++abi", "-lunwind",
+  "--no-dependent-libraries",
+]
+