sys-libs/glibc: preserve /usr/lib witk keepdir

Today crossdev does not install baselayout into /usr/${CTARGET}.
As a result /usr/${CTARGET}/usr/lib was not created by any ebuilds.
glibc ebuild used to create /usr/lib but recently added
install-qa-check.d/95empty-dirs by portage broke that assumption.

This change uses keepdir to ensure presense of /usr/${CTARGET}/usr/lib.
Longer term crossdev will attempt to use baselayout.

Reported-by: Vadim A. Misbakh-Soloviov <git@mva.name>
Bug: https://bugs.gentoo.org/652724
Package-Manager: Portage-2.3.43, Repoman-2.3.10

sys-libs/glibc/glibc-2.27-r5.ebuild

@@ -1215,10 +1215,8 @@ glibc_do_src_install() {
 		# gcc likes to use relative paths to get to its multilibs like
 		# /usr/lib/../lib64/.  So while we don't install any files into
 		# /usr/lib/, we do need it to exist.
-		cd "${ED}"$(alt_libdir)/..
-		[[ -e lib ]] || mkdir lib
-		cd "${ED}"$(alt_usrlibdir)/..
-		[[ -e lib ]] || mkdir lib
+		keepdir $(alt_prefix)/lib
+		keepdir $(alt_prefix)/usr/lib
 
 		dosym usr/include $(alt_prefix)/sys-include
 		return 0

sys-libs/glibc/glibc-9999.ebuild

@@ -1219,10 +1219,8 @@ glibc_do_src_install() {
 		# gcc likes to use relative paths to get to its multilibs like
 		# /usr/lib/../lib64/.  So while we don't install any files into
 		# /usr/lib/, we do need it to exist.
-		cd "${ED}"$(alt_libdir)/..
-		[[ -e lib ]] || mkdir lib
-		cd "${ED}"$(alt_usrlibdir)/..
-		[[ -e lib ]] || mkdir lib
+		keepdir $(alt_prefix)/lib
+		keepdir $(alt_prefix)/usr/lib
 
 		dosym usr/include $(alt_prefix)/sys-include
 		return 0