buildroot

zsh: don't use host pcre-config

Commit 5e05faec7b4 (zsh: use the correct target pcre-config) set
ac_cv_prog_PCRECONF to the location of staging pcre-config. Unfortunately zsh
configure script does not actually use this variable when running pcre-config.
Complete the fix with a patch that makes use of ac_cv_prog_PCRECONF.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>