Summary: Added extra check that windows sdk is valid.
Reviewed-by: tbell, ohrstrom, ohair

Summary: Removing trailing backslash from LIB and INCLUDE.
Reviewed-by: ohrstrom, ohair

Summary: Build-infra project integration. Multiple authors on this work: erikj and ihse primarily, also changes from ohair, tbell, and dholmes. Special credit to ohstrom for his smartjavac work.
Reviewed-by: erikj, ihse, dholmes, tbell