<iso646.h>: Avoid conflicts w/ C++ keywords.

Fix whitespace too.

Obtained-from:   FreeBSD
Bring in FreeBSD's msun code for our libm.

Our current libm is a mix of NetBSD and FreeBSD.  To ease
maintainability, sync with FreeBSD as requested by John Marino.

Obtained-from:   FreeBSD
Add <tgmath.h>.

Obtained-from:   FreeBSD
Stop overwriting /etc/services.

Users should be able to configure their services database, so those
changes shouldn't be blown away when they do a make upgrade.

Dragonfly-bug: <http://bugs.dragonflybsd.org/issues/2564>