auto merge of #7796 : thomaslee/rust/issue-6247, r=z0w0

This closes #6247 by simply ensuring librustllvm.so gets installed to the target lib directory in addition to the host lib directory.

Author: bors

mk/install.mk

@@ -97,6 +97,7 @@ install-target-$(1)-host-$(2): LIB_DESTIN_DIR=$$(PTL$(1)$(2))
 install-target-$(1)-host-$(2): $$(CSREQ$$(ISTAGE)_T_$(1)_H_$(2))
 	$$(Q)mkdir -p $$(PTL$(1)$(2))
 	$$(Q)$$(call INSTALL_LIB,$$(CFG_RUNTIME_$(1)))
+	$$(Q)$$(call INSTALL_LIB,$$(CFG_RUSTLLVM_$(1)))
 	$$(Q)$$(call INSTALL_LIB,$$(STDLIB_GLOB_$(1)))
 	$$(Q)$$(call INSTALL_LIB,$$(EXTRALIB_GLOB_$(1)))
 	$$(Q)$$(call INSTALL_LIB,$$(LIBRUSTC_GLOB_$(1)))