[libc] Bring libc in-tree

Moving libc from its separate repo into this one, minor resulting build
fixes, and a hacky way to add -I for libc headers in builds.

scripts/templates/target.user.j2

@@ -23,6 +23,7 @@ ccflags = $ccflags $
     -D__ELF__ $
     -D__JSIX__ $
     -isystem${srcroot}/sysroot/include $
+    -isystem${srcroot}/src/libraries/libc/include $
     --sysroot="${srcroot}/sysroot"
 
 cxxflags = $cxxflags $
@@ -38,9 +39,6 @@ ldflags = $ldflags $
     --sysroot="${srcroot}/sysroot" $
 	-L "${srcroot}/sysroot/lib" $
 
-libs = $libs $
-	-lc
-
 {% endblock %}
 
 # vim: ft=ninja et ts=4 sts=4 sw=4