Revert "package/php: fix building pcre extension"

Revert "package/php: fix building pcre extension"

This reverts commit 745f884e41b5f350296e8448f5fc31d20f67a077.

This was the wrong fix: issue is that php moves from pcre to pcre2 since
version 7.3.0 and
http://github.com/php/php-src/commit/a5bc5aed71f7a15f14f33bb31b8e17bf5f327e2d

This patch will always disable external pcre2 support and raise a build
failure when toolchaine does not have pthread

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>