It is very likely a documentation bug that the first argument to translit is not double quoted. Even if STRCASE is a valid macro, expanding it does not follow POLA.
changequote([,])dnl define([gl_STRING_MODULE_INDICATOR], [dnl comment GNULIB_[]translit([$1], [a-z], [A-Z])=1dnl ])dnl gl_STRING_MODULE_INDICATOR([strcase]) => GNULIB_STRCASE=1 http://www.gnu.org/software/m4/manual/m4.html