Mark all atomic functions as Q_DECL_NOTHROW

Mark all atomic functions as Q_DECL_NOTHROW

Actually, only the "new" atomics are marked. The old implementation,
based on qoldbasicatomic.h is unchanged, but should still work without a
problem.

The following configurations were tested and do work:
 - x86 64-bit
 - x86 32-bit
 - generic GCC
 - generic C++11 std::atomic
 - bootstrap
 - ARMv6 and 7
 - MIPS
 - MSVC 2010 32-bit
 - MSVC 2010 64-bit

The only two configurations untested are IA-64 and ARMv5. Except for
MSVC, all configurations were tested with GCC 4.6 (MIPS and ARM) and 4.7
(x86 and generics).

Change-Id: Iecbfeacd9d20b535453e91335165e9a221e0b47e
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>