[7.3.x] Fix gdb print extreme fp number

See b.android.com/69203.  GDB before 7.6 (including gdb-7.3.x in NDK) has
issues printing extrem fp number:

    (gdb) p 1e39f
    $1 = -5.5173927e-39

    When it should print
    $1 = inf

Backport fix: https://sourceware.org/ml/gdb-patches/2012-06/msg00452.html

    2012-07-25  Joel Brobecker  <brobecker@adacore.com>

         * doublest.c (convert_doublest_to_floatformat): If the exponent
         is too small, treat the value as zero.  If the exponent is too
         large, treat the value as infinity.

Change-Id: If0eb43f9e090bdcb8244fb5f8b4ba10a2272bd14