Revert "Reland "Bump the global default C standard to gnu23.""

This reverts commit cfb576268173f49f711b0bedab05fe879c0a1621.

Reason for revert: DroidMonitor: Potential culprit for http://b/397694474 - verifying through ABTD before revert submission. Please note that this is part of our standard investigation process and does not necessarily mean your CL will be reverted.

Change-Id: Ib84fb17a23726e7081494766927b52e0f04997ab
diff --git a/cc/config/global.go b/cc/config/global.go
index ddb4d85..b19682d 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -380,7 +380,7 @@
 		"-w",
 	}
 
-	CStdVersion               = "gnu23"
+	CStdVersion               = "gnu17"
 	CppStdVersion             = "gnu++20"
 	ExperimentalCStdVersion   = "gnu2x"
 	ExperimentalCppStdVersion = "gnu++2b"