[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.user.yaml

@@ -5,11 +5,6 @@ ccflags: [
   "--target=x86_64-jsix-elf",
   "-fno-omit-frame-pointer",
   "-fno-stack-protector",
-  "-fpic",
-  "-fpie",
-
-  "-g3",
-  "-ggdb",
 
   "-fvisibility=hidden",
   "-fvisibility-inlines-hidden",
@@ -19,7 +14,10 @@ ccflags: [
   "-U__linux",
   "-U__linux__",
 
-  "--sysroot='${source_root}/sysroot'" ]
+  "--sysroot='${source_root}/sysroot'",
+
+  "-fpic"
+]
 
 
 cxxflags: [
@@ -28,7 +26,6 @@ cxxflags: [
   ]
 
 ldflags: [
-  "-g",
   "-m", "elf_x86_64",
   "--sysroot='${source_root}/sysroot'",
   "--no-eh-frame-hdr",
@@ -36,6 +33,5 @@ ldflags: [
   "-z", "separate-code",
   "-lc++", "-lc++abi", "-lunwind",
   "--no-dependent-libraries",
-  "--dynamic-linker", "/tools/ld.so",
 ]