Address warnings across liblwgeom/ and postgis/

[Algunenano]

Address warnings in the liblwgeom and postgis folders that appear with GCC or Clang.

PR: ​https://github.com/postgis/postgis/pull/207

Main issues were:

• Unused parameters: I've removed when it was clear or used __attribute__((__unused__)) if there might be a reason (consistency / configure versions) for the parameters to stay.
• Some int vs int32_t issues.
• Some fall through statements.

[komzpa]

In 16377:

Address warnings across liblwgeom/ and postgis/

Patch by Raúl Marín Rodríguez

Closes ​https://github.com/postgis/postgis/pull/207
Closes #4014