intl: Fix a build error on Android.

intl: Fix a build error on Android.

The declaration in Android's <math.h>
  long double frexpl(long double, int*) __RENAME_LDBL(frexp, 3, 21);
has the effect that frexpl.o defines the symbol _libintl_frexp, not
_libintl_frexpl, if config.h contains
  #define frexp _libintl_frexp
  #define frexpl _libintl_frexpl

* gettext-runtime/intl/configure.ac:
If REPLACE_FREXP is 1, don't redirect frexp to _libintl_frexp.
If REPLACE_FREXPL is 1, don't redirect frexpl to _libintl_frexp.