gcclikecompiler: Fix execution of compiler qprocess under windows
Rather than passing null device as input file to the compiler,
"-" is passed as argument which makes the compiler take input from
stdin, then qprocess' standard input file is set to QProcess:nullDevice()
to make it read eof.
Note that it fixes standard includes not being passed to language plugin if
clang is set as default compiler under windows.
Reviewers: KDevelop, kfunk
Reviewed By: KDevelop, kfunk
Subscribers: kfunk, brauch, kdevelop-devel
Differential Revision: https://phabricator.kde.org/D8831