mk: Don't install host rlibs

You rarely want to statically link against librustc and friends, so there's no
real reason to install the rlib version of these libraries, especially because
the rlibs are massive.

mk/prepare.mk

@@ -16,7 +16,7 @@
 #
 # It requires the following variables to be set:
 #
-#   PREPARE_HOST - the host triple 
+#   PREPARE_HOST - the host triple
 #   PREPARE_TARGETS - the target triples, space separated
 #   PREPARE_DEST_DIR - the directory to put the image
 
@@ -172,7 +172,10 @@ prepare-target-$(2)-host-$(3)-$(1): \
         $$(if $$(findstring $(2),$$(CFG_HOST)), \
           $$(foreach crate,$$(HOST_CRATES), \
             $$(TLIB$(1)_T_$(2)_H_$(3))/stamp.$$(crate)),)
-# Only install if this host and target combo is being prepared
+# Only install if this host and target combo is being prepared. Also be sure to
+# *not* install the rlibs for host crates because there's no need to statically
+# link against most of them. They just produce a large amount of extra size
+# bloat.
 	$$(if $$(findstring $(1), $$(PREPARE_STAGE)),\
       $$(if $$(findstring $(2), $$(PREPARE_TARGETS)),\
         $$(if $$(findstring $(3), $$(PREPARE_HOST)),\
@@ -182,8 +185,7 @@ prepare-target-$(2)-host-$(3)-$(1): \
             $$(call PREPARE_LIB,$$(call CFG_RLIB_GLOB,$$(crate))))\
           $$(if $$(findstring $(2),$$(CFG_HOST)),\
             $$(foreach crate,$$(HOST_CRATES),\
-              $$(call PREPARE_LIB,$$(call CFG_LIB_GLOB_$(2),$$(crate)))\
-              $$(call PREPARE_LIB,$$(call CFG_RLIB_GLOB,$$(crate)))),)\
+              $$(call PREPARE_LIB,$$(call CFG_LIB_GLOB_$(2),$$(crate)))),)\
           $$(call PREPARE_LIB,libmorestack.a) \
           $$(call PREPARE_LIB,libcompiler-rt.a),),),)
 endef