llex: fix lconv struct for bionic (android)

'struct lconv' has no member named 'decimal_point'

In fact this struct is empty on Android (4.4.4)

Else, all build fine, as you can see on my git variant :
http://github.com/tpruvot/android_external_lua/blob/cm-11.0/Android.mk

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>