Fix arch detection when cross compiling on Windows

Fix arch detection when cross compiling on Windows

When trying to detect the target architecture, configure.exe will look for a
file called 'arch.exe'. However, in some situations such as when
cross-compiling on a Windows host to a Unix host, and depending on the
toolchain being used, the output file generated by config.tests/arch may
simply be called "arch" instead of "arch.exe", causing configure.exe to fail.
This patches configure.exe to handle both naming schemes.

Change-Id: I5798f716d732388c707564d4d45c4887ab3d3d9f
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>