iOS: Propagate xcodebuild exit-code from makefile wrapper

Without bash's pipefail option we would end up with the exit code of
grep. Since we don't know which shell the user is running, we have
to explicitly call bash.

Change-Id: Ic3f6db0af9bb90a58001ccfbf9d6d21b6c9c9634
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

mkspecs/features/ios/default_post.prf

@@ -19,7 +19,7 @@ equals(TEMPLATE, app) {
 
         # We use xcodebuild to do the actual build, but filter out the verbose
         # output that shows all environment variables for each build step.
-        xcodebuild_build.commands = "@xcodebuild build | grep -v setenv"
+        xcodebuild_build.commands = "@bash -o pipefail -c 'xcodebuild | grep -v setenv'"
         QMAKE_EXTRA_TARGETS += xcodebuild_build
         all.depends = xcodebuild_build
         QMAKE_EXTRA_TARGETS += all