Added a bounch of locale fixes.

Added a bounch of locale fixes.

* extra/locale/gen_wc8bit.c: use strrchr to parse locale
  name to handle the case in which it contains a '.' character
  like ANSI_X3.4-1968

* include/locale.h: use __UCLIBC_HAS_XLOCALE__ to control
  inclusion of xlocale.h only

* libc/misc/ctype/ctype.c: add missing weak_alias for
  __tolower_l and __toupper_l

* libc/misc/locale/locale.c: use strcasecmp (case insensitive)
  for utf-8 locale name.

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>