lib: avoid pragma usage in inspect-fs-windows

pragma GCC diagnostic is a gcc 4.6+ feature, compilation fails with
older compilers:

inspect-fs-windows.c: In function 'map_registry_disk_blob':
inspect-fs-windows.c:502: error: #pragma GCC diagnostic not allowed inside functions
inspect-fs-windows.c:503: error: #pragma GCC diagnostic not allowed inside functions
inspect-fs-windows.c:505: error: #pragma GCC diagnostic not allowed inside functions
make[3]: *** [libguestfs_la-inspect-fs-windows.lo] Error 1

Use memcpy instead of pragma to fix compile error.

Signed-off-by: Olaf Hering <olaf@aepfle.de>