Roll external/abseil_cpp/ 768f75440..6c5a17577 (76 commits)

abseil/abseil-cpp@768f754...6c5a175

Created with:
  roll-dep external/abseil_cpp

Author: GitHub Actions[bot]

DEPS

@@ -3,7 +3,7 @@ use_relative_paths = True
 vars = {
   'github': 'https://github.com',
 
-  'abseil_revision': '768f75440fe009e2b7e0c3e1f247f67970c83975',
+  'abseil_revision': '6c5a175774752699ac20c5b1a329efd4710b2809',
 
   'effcee_revision': '514b52ec61609744d7e587d93a7ef9b60407ab45',