etc: rework of how libuv is integrated into the build

- thanks to work in libuv's upstream, we can call libuv's Makefile directly
with parameters, instead of descending in gyp-uv madness and generating
our own.

configure

@@ -578,7 +578,7 @@ do
   make_dir rt/$t
   for i in                                          \
     isaac linenoise sync test arch/i386 arch/x86_64    \
-    libuv libuv/src/ares libuv/src/eio libuv/src/ev
+    libuv
   do
     make_dir rt/$t/$i
   done