Os::Task::taskRoutine not compliant with POSIX Thread Entrypoint

[Joshua-Anderson]

F´ Version	devel
Affected Component	Os

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Problem Description

F Prime's threads have no return value, which was likely done to provide greater compatibility across different platforms.
However, POSIX threads are expected to return a void *. This causes compilation errors, since returning void when a return value is expected is undefined behavior.

We should either wrap the user provided taskRoutine with another function that returns 0 or change taskRoutine to expect a return value.

From compiling with -Wextra:

/fprime/Os/Posix/Task.cpp: In member function ‘Os::Task::TaskStatus Os::Task::start(const Fw::StringBase&, NATIVE_INT_TYPE, NATIVE_INT_TYPE, NATIVE_INT_TYPE, Os::Task::taskRoutine, void*, NATIVE_INT_TYPE)’:
/fprime/Os/Posix/Task.cpp:119:58: error: cast between incompatible function types from ‘Os::Task::taskRoutine’ {aka ‘void (*)(void*)’} to ‘pthread_func_ptr’ {aka ‘void* (*)(void*)’} [-Werror=cast-function-type]
  119 |         stat = pthread_create(tid,&att,(pthread_func_ptr)routine,arg);