configure: do not redefine _REENTRANT
configure: do not redefine _REENTRANT

This fixes warnings with PulseAudio and with MingW.

(cherry picked from commit 8dcec7992236b8d2528ab088554766058d71505c)
Signed-off-by: Jean-Baptiste Kempf <7b85a41a628204b76aba4326273a3ccc74bd009a@videolan.org>

jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2