Fixed the path that the Python binding .cpp file is generated into.
Fixed the path that the Python binding .cpp file is generated into.

Xcode uses a variety of environment variables to specify where built products
should go.  While CONFIGURATION_BUILD_DIR is usually safe, the more accurate
variable to use is BUILT_PRODUCTS_DIR.  Although this does not affect running
'xcodebuild' with the Debug configuration, for example, it can matter when using
'xcodebuild install,' where the two may be different.

This patch uses the more accurate BUILT_PROUDUCTS_DIR when telling the Python
wrapper generation script where to put the generated .cpp file.  It should not
have any effect on the vast majority of builds; please let me know if it causes
any trouble.

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb