Fix msync() redefinition for noMMU build
An architecture that _may_ have a MMU (and thus implements
the msync syscall), but for which the kernel and uClibc are built as
noMMU, we have a stub for msync.
Thanks to Steven J. Magnani for noticing.
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>