Reland^2 "Bump the global default C standard to gnu23."

This reverts commit b358e4fb8255f839e5a8f269a32bc78ec196005e.

Change-Id: Ibf847c0a7077689d07501d93702e18ec8b1e8e61
diff --git a/cc/config/global.go b/cc/config/global.go
index b19682d..ddb4d85 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -380,7 +380,7 @@
 		"-w",
 	}
 
-	CStdVersion               = "gnu17"
+	CStdVersion               = "gnu23"
 	CppStdVersion             = "gnu++20"
 	ExperimentalCStdVersion   = "gnu2x"
 	ExperimentalCppStdVersion = "gnu++2b"