tool: use local LC_ALL=C instead of LC_COLLATE=C

We used to export 'LC_COLLATE=C' for the environment of Genode tools. This was
meant to ensure that sorting is always done C-style and not dependent on the
users locale settings. This is required, for instance, to ensure that the same
archive always yields the same hash.

However, 'export LC_COLLATE=C' is not sufficient. It can be outruled by an
'LC_ALL' setting in the users environment. The manual of 'sort' recommends to
set 'LC_ALL=C' locally if you want reliable results and this is what this
commit does. Furthermore it removes the former 'export LC_COLLATE=C'
directives.

Note that I couldn't find a way to set 'LC_ALL' local to 'exec ... sort' in
TCL. This is why I set it global instead using TCLs 'env' array.

Note that the Make directive '$(sort ...)' and the TCL directive 'lsort',
unlike the Shell directive 'sort', are not affected by the users locale
settings.

Fixes #4144

tool/depot/mk/common.inc

@@ -32,4 +32,4 @@ EMPTY :=
 file_content = $(if $(wildcard $1),$(shell cat $1),)
 
 # Force stable sorting order
-export LC_COLLATE=C
+SORT := LC_ALL=C sort

tool/depot/mk/extract.inc

@@ -214,8 +214,8 @@ _check_hash: $(DEPOT_ARCHIVE_DIR).hash checked_recipe_hash_value_exists
 # command).
 #
 HASH_CMD := cd $(DEPOT_ARCHIVE_DIR); \
-            (find . -type f | sort; \
-             find . -type f | sort | xargs -d '\n' cat) \
+            (find . -type f | $(SORT); \
+             find . -type f | $(SORT) | xargs -d '\n' cat) \
             | $(HASHSUM) | sed "s/ .*//"
 
 #

tool/depot/mk/extract_post_dependencies.inc

@@ -34,7 +34,7 @@ endif
 #
 # \param $1  absolute file path
 #
-sorted_file_content = $(if $(wildcard $1),$(shell cat $1 | sort -u),\
+sorted_file_content = $(if $(wildcard $1),$(shell cat $1 | $(SORT) -u),\
                                           $(error Failed to read file $1))
 
 #