Fixed bug EXT-6399 (System locale is the same for all languages).

Problem:
* English locale was set for all languages.
* Specifying a correct locale didn't affect anything, including date/time formatting.

My investigation has shown that LLStringUtil was instantiated twice: in the
main binary and in libllcommon.so.
Because LLStringUtil::setLocale() was called from newview and getLocale()
was called from llcommon, they effectively used *different* instances of
LLStringUtil::sLocale. Hence getLocale() always returned empty string.

This seems to be caused by get/setLocale() methods not being dllexported.

The fix instantiates get/setLocale() and sLocale in llcommon and exposes
them to use from newview (i.e. prevents multiple instantiation).

Besides, I specified correct locale names for all languages and platforms.

Reviewed by Leyla: https://codereview.productengine.com/secondlife/r/104/

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branch : product-engine