Fix --libdir installs

Rather than modifying the installer to disable directory rewriting,
this patch modifies the directory structure passed to the installer so
that the rewriting gives the correct results.  This means that if a
non-standard --libdir is passed to configure then the same --libdir
option (relative to the --prefix) must be passed to the install
script.  In the `make install` case this is handled automatically.
Binary distributions are generally generated using the default
--libdir and then have paths optionally rewritten by the installer,
which should continue to work.

This has the advantage of not complicating the installer interface
intended for end-user use.

Fixes #29561

Author: wthrowe

mk/prepare.mk

@@ -104,6 +104,11 @@ prepare-host-tool-$(1)-$(2)-$(3)-$(4): prepare-maybe-clean-$(4) \
         $$(call PREPARE_MAN,$(1).1),),)
 endef
 
+# Libraries are compiled using the --libdir provided to configure, but
+# we store them in the tarball using just "lib" so that the install
+# script can then rewrite them back to the correct path.
+PREPARE_TAR_LIB_DIR = $(patsubst $(CFG_LIBDIR_RELATIVE)%,lib%,$(1))
+
 # For host libraries only install dylibs, not rlibs since the host libs are only
 # used to support rustc and rustc uses dynamic linking
 #
@@ -115,7 +120,7 @@ define DEF_PREPARE_HOST_LIB
 prepare-host-lib-$(1)-$(2)-$(3)-$(4): \
 	PREPARE_WORKING_SOURCE_LIB_DIR=$$(HLIB$(2)_H_$(3))
 prepare-host-lib-$(1)-$(2)-$(3)-$(4): \
-	PREPARE_WORKING_DEST_LIB_DIR=$$(PREPARE_DEST_DIR)/$$(HLIB_RELATIVE$(2)_H_$(3))
+	PREPARE_WORKING_DEST_LIB_DIR=$$(PREPARE_DEST_DIR)/$$(call PREPARE_TAR_LIB_DIR,$$(HLIB_RELATIVE$(2)_H_$(3)))
 prepare-host-lib-$(1)-$(2)-$(3)-$(4): prepare-maybe-clean-$(4) \
                                  $$(foreach dep,$$(RUST_DEPS_$(1)),prepare-host-lib-$$(dep)-$(2)-$(3)-$(4)) \
                                  $$(HLIB$(2)_H_$(3))/stamp.$(1) \
@@ -195,7 +200,7 @@ define DEF_PREPARE
 
 prepare-base-$(1)-%: PREPARE_SOURCE_MAN_DIR=$$(S)/man
 prepare-base-$(1)-%: PREPARE_DEST_BIN_DIR=$$(PREPARE_DEST_DIR)/bin
-prepare-base-$(1)-%: PREPARE_DEST_LIB_DIR=$$(PREPARE_DEST_DIR)/$$(CFG_LIBDIR_RELATIVE)
+prepare-base-$(1)-%: PREPARE_DEST_LIB_DIR=$$(PREPARE_DEST_DIR)/$$(call PREPARE_TAR_LIB_DIR,$$(CFG_LIBDIR_RELATIVE))
 prepare-base-$(1)-%: PREPARE_DEST_MAN_DIR=$$(PREPARE_DEST_DIR)/share/man/man1
 
 prepare-base-$(1)-target: prepare-target-$(1)