Multiple signum definitions

[Raul Marin]

There are 2 different definitions of the signum function, one in lwgeodetic.h and another in lwalgorithm.c.

Fixed in MR: ​https://github.com/postgis/postgis/pull/150

[pramsey]

In 15900:

Combine multiple signum definitions (2.2)
(References #3878)

[pramsey]

In 15901:

Combine multiple signum definitions (2.3)
(References #3878)

[pramsey]

In 15902:

Combine multiple signum definitions (2.4)
(References #3878)

[pramsey]

In 15903:

Combine multiple signum definitions
(Closes #3878)