With zexy fixed on mingw64, revert external-tests.pd to what it was before rev. 2f3c815a.

6 jobs for release_2.15.2 in 109 minutes and 15 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Test
canceled debian_stretch_x86_64_deb #22506
debian stretch x86_64

passed osx_10.11_x86_64_dmg #22508
osx v10.11 dmg

00:17:57

passed osx_10.8_x86_64_dmg #22509
v10.8 dmg osx

00:19:52

canceled raspbian_stretch_armv7l_deb #22511
raspbian arm stretch

passed ubuntu_16.04_x86_64_deb #22507
ubuntu v16.04 x86_64

00:33:46

passed windows_i386_innosetup #22510
windows i386

01:49:14