php5: temporarily restore pecl.mk to reduce unnecessary oldpackages breakage from the move to github

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/packages@42779 3c298f89-4303-0410-b956-a3cf2f4a3e73