dosfs: Support ctime and mtime

Implement ctime and mtime updates according to POSIX.  The ctime is
mapped to the FAT create time and date.  The mtime is mapped to the FAT
last modified time and date.  For the atime use the mtime for
simplicity.
Revert "fstests/mdosfs_fstime: Remove test"

This reverts commit bdcf4102f71d1bc2a50f23d2d425d85c24ec0900.
dosfs: Write meta-data only if it changed
bsp/sparc: Ensure that data cache snooping is enabled

Check that data cache snooping exists and is enabled on all cores.
testsuites: Move include for C++ compatibility
bsps: Move extern "C" to not cover includes

Some includes may use C++ and this conflicts if surrounded extern "C".
bsp/leon3: Fix LEON3_mp_irq definition

Provide it also if RTEMS_MULTIPROCESSING is defined.