javac warns whenever -source is used with a version that does not
match javac, because it wants an rt.jar provided for the given
source level. We are not using -source to prevent usage of APIs
that don't exist in the newer rt.jar, so hide the messages.
Test: javac_wrapper_test.go
Change-Id: Ic94b61767436848fc164e377dc3cc5a63726f1cf
Piping the output of javac through a filter makes it hard to capture
the exit status. Convert it to a wrapper that executes javac and
propagates the exit status.
Bug: 36666657
Test: javac_wrapper_test
Change-Id: I9b56cc3794023aabc9328138a68830e26e980f97
