iOS: Don't mangle QT_ARCH when being more specific about what arch to build

On iOS the compiler expects archs like armv6, armv7, armv7s when passed the
-arch flag, or when the ARCHS Xcode variable is set. Instead of mangling
QT_ARCH, which is used other places and assumed to match the values
provided by the arch.test, we use our own variable.

Change-Id: I05e10be8d69dd4d7cbcef04640fef99f1efb253d
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>
qmake: do not write timestamps to generated Makefiles

These timestamps were useless and broken on non-ascii locales.

Change-Id: Iad08eb0f5dfd5e86f6451d6572365d0c080e6115
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>