gauche: fix build with uClibc

gauche: fix build with uClibc

As gauche bundles bdwgc, it hit the same uclibc build issue fixed in commit
9b04ae71c5e4c (package/bdwgc: fix uclibc build after bump to 7.6.0). Apply the
upstream bdwgc fix for that.

Fixes:
http://autobuild.buildroot.net/results/ebc/ebc70579a94d260fecf05fe4150eebcc59d3b5fb/
http://autobuild.buildroot.net/results/e1b/e1b2ad89787c345cf8817f6d8436ff52a151c5a6/
http://autobuild.buildroot.net/results/f39/f396b996a59db79f7a0926aec49c488c3a2797a0/

Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Cc: Hiroshi Kawashima <kei-k@ca2.so-net.ne.jp>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>