Switch to cecil branch with better pdb handling

diff --git a/external/cecil b/external/cecil
index 74ab08331c603d45932fa825c49329e124c2c77a..8180cef874eb1d631eac3ad186cc28e27165f44f 160000 (submodule)
--- a/external/cecil
+++ b/external/cecil
@@ -1 +1 @@
-Subproject commit 74ab08331c603d45932fa825c49329e124c2c77a
+Subproject commit 8180cef874eb1d631eac3ad186cc28e27165f44f