Makefile: do not override LC_CTYPE

Setting LC_CTYPE=C breaks localized messages in some setups. With only
LC_COLLATE=C and LC_NUMERIC=C, we get almost all we need, except for not
so defined character classes and tolower()/toupper(). The former is not
a big issue, because we can assume that e.g. [:alpha:] will always
include a-zA-Z and we only ever process ASCII input. The latter seems
only affect arch/sh/tools/gen-mach-types, which we can handle separately.

So after this patch the meaning of ranges like [a-z], the behavior of
sort and join, etc. should be the same everywhere and at the same time
gcc should be able to print localized waring and error messages.
LC_NUMERIC=C might not be necessary, but setting it doesn't hurt.

Reported-by: Simon Horman <horms@verge.net.au>
Reported-by: Sergei Trofimovich <slyfox@inbox.ru>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Tested-by: Simon Horman <horms@verge.net.au>
Tested-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>