Android: correct module name for _math

This module was named improperly during the migration. Correct the name
to `_math`.

Author: compnerd

Runtimes/Overlay/Android/Math/CMakeLists.txt

@@ -2,7 +2,7 @@
 add_library(swift_math
   Math.swift)
 set_target_properties(swift_math PROPERTIES
-  Swift_MODULE_NAME math)
+  Swift_MODULE_NAME _math)
 target_link_libraries(swift_math PRIVATE
   SwiftAndroid
   swiftCore)