projectexplorer/qmake-makestep: parse output of xcodebuild

Xcodebuild (used by default for ios and optionally on mac) redirects all
compile errors to stdout.
This breaks the detection of errors.
Redirect stdout to stderr if within xcodebuild.

Change-Id: I60fd21a7b075fbfc29c99a10debf34e20487c4df
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
support the latest g++ on mac

the latest g++ on mac is really clang with a compatibility frontend,
and claims to be clang and support all the features clang does
with -std=c++0x (which qmake by default passes in).
But if you link libstdc++ (again the default) then the library has
several gaps. Catch that.

Change-Id: I8387f8fdcfc7639538e576a2e93b2301e07086cd
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>