toolchain helpers: introduce function relpath_prefix

The helper function copy_toolchain_sysroot has some logic to transform a
path into a number of '../' components based on the depth of that path.

As this same logic will be needed in another place in a subsequent patch,
extract it into a separate helper relpath_prefix.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

toolchain/helpers.mk

@@ -122,11 +122,7 @@ copy_toolchain_sysroot = \
 			cp -a $${SYSROOT_DIR}/usr/include $(STAGING_DIR)/usr ; \
 		fi ; \
 		mkdir -p `dirname $(STAGING_DIR)/$${ARCH_SUBDIR}` ; \
-		relpath="./" ; \
-		nbslashs=`printf $${ARCH_SUBDIR} | sed 's%[^/]%%g' | wc -c` ; \
-		for slash in `seq 1 $${nbslashs}` ; do \
-			relpath=$${relpath}"../" ; \
-		done ; \
+		relpath="$(call relpath_prefix,$${ARCH_SUBDIR})./" ; \
 		ln -s $${relpath} $(STAGING_DIR)/$${ARCH_SUBDIR} ; \
 		echo "Symlinking $(STAGING_DIR)/$${ARCH_SUBDIR} -> $${relpath}" ; \
 	fi ; \
@@ -419,3 +415,22 @@ check_toolchain_ssp = \
 gen_gdbinit_file = \
 	mkdir -p $(STAGING_DIR)/usr/share/buildroot/ ; \
 	echo "set sysroot $(STAGING_DIR)" > $(STAGING_DIR)/usr/share/buildroot/gdbinit
+
+# Given a path, determine the relative prefix (../) needed to return to the
+# root level. Note that the last component is treated as a file component; use a
+# trailing slash to force treating it as a directory. Examples:
+#     relpath_prefix(lib32) = ""
+#     relpath_prefix(lib32/octeon2) = "../"
+#     relpath_prefix(lib32/octeon2/) = "../../"
+#
+# $1: input path
+define relpath_prefix
+$$( \
+	prefix="" ; \
+	nbslashs=`printf $1 | sed 's%[^/]%%g' | wc -c` ; \
+	for slash in `seq 1 $${nbslashs}` ; do \
+		prefix=$${prefix}"../" ; \
+	done ; \
+	printf "$$prefix" ; \
+)
+endef