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/builddir/build.mk

@@ -67,9 +67,6 @@ export ECHO             ?= echo -e
 export CONTRIB_DIR
 export BOARD
 
-# Force stable sorting order
-export LC_COLLATE=C
-
 #
 # Convert user-defined directories to absolute directories
 #