AAPT2: Allow the ';' separator on Windows for split args

Bug: 36870463
Test: manual (wine)
Change-Id: I8a38545a3cac9354b41858e1840b197b60925c03
diff --git a/tools/aapt2/cmd/Optimize.cpp b/tools/aapt2/cmd/Optimize.cpp
index 8f8e0c8..e99ee8a 100644
--- a/tools/aapt2/cmd/Optimize.cpp
+++ b/tools/aapt2/cmd/Optimize.cpp
@@ -302,7 +302,8 @@
                             &configs)
           .OptionalFlagList("--split",
                             "Split resources matching a set of configs out to a "
-                            "Split APK.\nSyntax: path/to/output.apk:<config>[,<config>[...]].",
+                            "Split APK.\nSyntax: path/to/output.apk;<config>[,<config>[...]].\n"
+                            "On Windows, use a semicolon ';' separator instead.",
                             &split_args)
           .OptionalSwitch("--enable-sparse-encoding",
                           "Enables encoding sparse entries using a binary search tree.\n"