Enable the experimental LLVM new pass manager

For walleye, the overall binary size is decreased by ~1.1%.

For Googlers, http://go/android-llvm-newpm

Test: build
Bug: 131855431
Change-Id: I6726cd3de0d528b773fb23eae1a7c5c360e29807

cc/config/clang.go

@@ -107,6 +107,9 @@ func init() {
 		// Help catch common 32/64-bit errors.
 		"-Werror=int-conversion",
 
+		// Enable the new pass manager.
+		"-fexperimental-new-pass-manager",
+
 		// Disable overly aggressive warning for macros defined with a leading underscore
 		// This happens in AndroidConfig.h, which is included nearly everywhere.
 		// TODO: can we remove this now?