Fix another misnomer.
* gettext-runtime/intl/Makefile.am (AM_CPPFLAGS): Set BUILDING_LIBRARY instead
of BUILDING_DLL.
* gettext-runtime/intl/intl-compat.c (SHLIB_EXPORTED): Test BUILDING_LIBRARY
instead of BUILDING_DLL.
* gettext-runtime/intl/printf.c (SHLIB_EXPORTED): Likewise.
* gettext-runtime/intl/setlocale.c (SHLIB_EXPORTED): Likewise.
