Update ABC

Author: mmicko

Makefile

@@ -142,7 +142,7 @@ bumpversion:
 # is just a symlink to your actual ABC working directory, as 'make mrproper'
 # will remove the 'abc' directory and you do not want to accidentally
 # delete your work on ABC..
-ABCREV = b4790a6
+ABCREV = d7ecb23
 ABCPULL = 1
 ABCURL ?= https://github.com/YosysHQ/abc
 ABCMKARGS = CC="$(CXX)" CXX="$(CXX)" ABC_USE_LIBSTDCXX=1 VERBOSE=$(Q)