* sysdeps/ieee754/ldbl-opt/nldbl-compat.h (NLDBL_DECL): Don't try
attribute_hidden here.
* sysdeps/ieee754/ldbl-opt/nldbl-vsyslog.c (vsyslog): Restore
attribute_hidden here.
* sysdeps/ieee754/ldbl-opt/nldbl-asprintf.c (__asprintf): Likewise.
* sysdeps/ieee754/ldbl-opt/nldbl-fprintf.c (fprintf): Likewise.
* sysdeps/ieee754/ldbl-opt/nldbl-qecvt.c (qecvt): Likewise.
* sysdeps/ieee754/ldbl-opt/nldbl-qfcvt.c (qfcvt): Likewise.
* sysdeps/ieee754/ldbl-opt/nldbl-qgcvt.c (qgcvt): Likewise.
* sysdeps/ieee754/ldbl-opt/configure.in: Use AC_TRY_COMPILE and
verify __LONG_DOUBLE_128__ predefine.
* sysdeps/ieee754/ldbl-opt/configure: Regenerated.