[BUG 2.3.0–CURRENT] input_method conflicts with -D_FORTIFY_SOURCE=2

[Ilya Zakharevich <nospam-abuse@ilyaz.org>]

For reference, see
    http://matrix.cpantesters.org/?dist=Math-Pari%202.030501
Clicking on yellow NetBSD rectanges leads to reports like this one:
    http://www.cpantesters.org/cpan/report/0cedc9f4-9892-11e8-bed3-aefc88cf513b
which gives

  cc -c -I pari-2.3.5/src -I pari-2.3.5/src/headers -I pari-2.3.5/src -I ./libPARI  -I ../pari-2.3.5/src -I ../pari-2.3.5/src/headers -I ../pari-2.3.5/src/graph -I .  -fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/pkg/include -D_FORTIFY_SOURCE=2 -O    -DVERSION=\"\"  -DXS_VERSION=\"\" -DPIC -fPIC -DPLOT_IS_TUNABLE -Derr=pari_err -DHAS_STAT -DHAS_OPENDIR -DASMINLINE -DGCC_INLINE -DDYNAMIC_PLOTTING -o es.o ../pari-2.3.5/src/language/es.c
  ../pari-2.3.5/src/language/es.c: In function 'file_input':
  ../pari-2.3.5/src/language/es.c:312:13: error: 'input_method' has no member named '__fgets_chk'
  *** Error code 1

⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜

Morale: using a field ->fgets which is a function pointer is not compatoble with -D_FORTIFY_SOURCE=2.
	      (checking https://pari.math.u-bordeaux.fr/cgi-bin/gitweb.cgi?p=pari.git;a=blob;f=src/language/es.c;h=42834091c9c893ba090ef0361657fce22a05b465;hb=HEAD#l448
	       shows that it is still the same now.

⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜⁜

Possible solution: change fgets to do_fgets.

Hope this helps,
Ilya