This is necessary to keep alignment between the client view of rig->state and the shared libarary view
Including PTHREAD functions in rig->state necessitated this as HAVE_PTHREAD only defined during hamlib compilation.
Clients including hamlib/rig.h did not pick up all the HAVE* config variable that control what gets included
https://github.com/Hamlib/Hamlib/issues/947
This is for consistency with other source fils, but gcc finds the include
file anyway (see https://gcc.gnu.org/onlinedocs/cpp/Search-Path.html)
Fixes:
rotators/amsat/if100.c:38:0: information: Include file: "math.h" not found. [missingInclude]