[locale.time.get] Replace 'ISO/IEC 9945' with 'POSIX'

We introduce POSIX as an alias for ISO/IEC 9945, and we use 'POSIX'
everywhere else.

Author: jensmaurer

source/locales.tex

@@ -3345,7 +3345,7 @@
 optionally followed by a modifier character,
 followed by a conversion specifier character, \tcode{format},
 together forming a conversion specification
-valid for the ISO/IEC 9945 function \tcode{strptime}.
+valid for the POSIX function \tcode{strptime}.
 If the number of elements in the range \range{fmt}{fmtend}
 is not sufficient to unambiguously determine
 whether the conversion specification is complete and valid,
@@ -3535,7 +3535,7 @@
 until it has extracted and assigned those \tcode{tm} members, and
 any remaining format characters,
 corresponding to a conversion directive appropriate for
-the ISO/IEC 9945 function \tcode{strptime},
+the POSIX function \tcode{strptime},
 formed by concatenating \tcode{'\%'},
 the \tcode{modifier} character, when non-NUL, and
 the \tcode{format} character.