make generic bits/fcntl.h shareable with 64-bit archs

make generic bits/fcntl.h shareable with 64-bit archs

the fcntl file locking command macro values in the existing generic
bits/fcntl.h were the "64" variants, requiring 64-bit archs that use
the "plain" variants to have their own bits/fcntl.h, even if they
otherwise use the common definitions for everything.

since commit 7cc79d10afd43811a486fd5e9fcdf8e45ac599e0 exposed
__LONG_MAX to all bits headers, we can now make the generic one common
between 32- and 64-bit archs.