Makefile.SH: record to be installed location in install_name

Instead of using $PWD, which is our build directory, use the to be
installed to location for the install_name on Darwin, soas to make it
point to something valid.

Signed-off-by: Fabian Groffen <grobian@gentoo.org>

--- a/Makefile.SH
+++ b/Makefile.SH
@@ -64,7 +64,7 @@
 				${revision}.${patchlevel}.${subversion}"
 		case "$osvers" in
 	        1[5-9]*|[2-9]*)
-			shrpldflags="$shrpldflags -install_name `pwd -P`/libperl.${revision}.${patchlevel}.dylib -Xlinker -headerpad_max_install_names"
+			shrpldflags="$shrpldflags -install_name \$(shrpdir)/libperl.${revision}.${patchlevel}.dylib -Xlinker -headerpad_max_install_names"
 			exeldflags="-Xlinker -headerpad_max_install_names"
 			;;
 		*)