Compile problem on cygwin

[rainer]

In src/sh_unix.c, function sh_unix_count_mlock(), unconditional reference is made to mutex_mlock, which does not exist if mlock() is not supported. Compiling will fail with:

x_sh_unix.c: In function `sh_unix_count_mlock':
x_sh_unix.c:4863: error: `mutex_mlock' undeclared (first use in this function)
x_sh_unix.c:4863: error: (Each undeclared identifier is reported only once
x_sh_unix.c:4863: error: for each function it appears in.)

This has been reported by Remco Landegge

[rainer]

Fixed in changeset [263].