8388115: Provide os::vm_min_address() for BSD

[bsdkurt]

https://bugs.openjdk.org/browse/JDK-8388115 requests implementation of os::vm_min_address() and os::vm_max_address() for BSD. os::vm_max_address() has not yet been merged into master but I have discussed the current BSD implementation of os::vm_min_address() with @tstuefe and came up with this change.

This PR is for correctness and does not change the return value of os::vm_min_address() on BSD because VM_MIN_ADDRESS is less then _vm_min_address_default on FreeBSD, OpenBSD and NetBSD. However, if some future architecture or future change to VM_MIN_ADDRESS makes it greater then _vm_min_address_default, the jdk is prepared for that change.

Of note is that _vm_min_address_default not only is the default value but also serves as a minimum value the JDK supports. When openjdk#31864 lands in master, I will follow up with BSD implementation of os::vm_max_address() that uses VM_MAXUSER_ADDRESS.

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[tstuefe]

Looks good to me (but I have no official role in the bsd project I think)

[snake66]

Looked at the discussion in the OpenJDK bug issue, and this change makes sense to me.