ClangCodeModel: discard stderr during clang detection
ClangCodeModel: discard stderr during clang detection

Otherwise we get useless noise in the General Messages pane if clang
isn't installed.

Change-Id: I8d34f79f1054b87b8530fcf6f253524a4c73897c
Reviewed-by: Oswald Buddenhagen <6a8868beda3e139b5ac22b2534a23d3e6ba81819@digia.com>
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@digia.com>

xianian/qt-creator,farseerri/git_code,farseerri/git_code,xianian/qt-creator,danimo/qt-creator,danimo/qt-creator,kuba1/qtcreator,martyone/sailfish-qtcreator,kuba1/qtcreator,martyone/sailfish-qtcreator,kuba1/qtcreator,xianian/qt-creator,amyvmiwei/qt-creator,maui-packages/qt-creator,xianian/qt-creator,kuba1/qtcreator,xianian/qt-creator,amyvmiwei/qt-creator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,danimo/qt-creator,danimo/qt-creator,maui-packages/qt-creator,maui-packages/qt-creator,farseerri/git_code,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,amyvmiwei/qt-creator,xianian/qt-creator,Distrotech/qtcreator,maui-packages/qt-creator,amyvmiwei/qt-creator,kuba1/qtcreator,danimo/qt-creator,amyvmiwei/qt-creator,danimo/qt-creator,maui-packages/qt-creator,AltarBeastiful/qt-creator,Distrotech/qtcreator,maui-packages/qt-creator,farseerri/git_code,xianian/qt-creator,danimo/qt-creator,kuba1/qtcreator,AltarBeastiful/qt-creator,danimo/qt-creator,martyone/sailfish-qtcreator,kuba1/qtcreator,AltarBeastiful/qt-creator,maui-packages/qt-creator,farseerri/git_code,danimo/qt-creator,Distrotech/qtcreator,xianian/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,farseerri/git_code,amyvmiwei/qt-creator,xianian/qt-creator,farseerri/git_code,Distrotech/qtcreator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,Distrotech/qtcreator,farseerri/git_code,Distrotech/qtcreator,kuba1/qtcreator,kuba1/qtcreator,Distrotech/qtcreator,AltarBeastiful/qt-creator,amyvmiwei/qt-creator