locale.c: White-space, comment, rearrange some #else

locale.c: White-space, comment, rearrange some #else

This file is full of conditional compilation, due to the fact that
locale support has been highly variable in the OSes Perl has operated
on.  This commit properly indents nested compiler directives, and makes
sure there is a blank line between the directives and real code.  I find
that much easier to read.  It also re-orders some

    #ifdef some_feature
        Many lines of code handling feature
    #else
        1 to 3 lines of trivial code to avoid compilation warnings
    #endif

to

    #ifndef some_feature
        1 to 3 lines of trivial code to avoid compilation warnings
    #else
        Many lines of code handling feature
    #endif

Otherwise the trivial code may be hundreds of lines from the original
'#if', which makes it hard to grok.

This commit also clarifies and fixes typos in comments, and removes some
obsolete comments.