Avoid warning race with creating 'ldscripts' directory during build.

In r204548 the 'rm -f ldscripts' was added likely due to reading the
conditional as 'else it is a file'. That seems unlikely though and
the more likely case is just that the directory hasn't been created yet.

Because this races with ,ssother scripts, use 'mkdir -p' which is a minimal
modification vs upstream to avoid the warning of 'File exists' if another
script creates it first. This could replace the 'test -d' as well but
then it's more unneeded change to the upstream script.

Sponsored by: EMC / Isilon Storage Division