epicsThreadExitMain() is deprecated

[tynanford]

While compiling pyDevSup against R7.0.10:

../devsupMain.cpp: In function ‘int main(int, char**)’:
../devsupMain.cpp:208:32: warning: ‘void epicsThreadExitMain()’ is deprecated [-Wdeprecated-declarations]
  208 |             epicsThreadExitMain();
      |             ~~~~~~~~~~~~~~~~~~~^~
In file included from ../devsupMain.cpp:65:
/usr/local/epics/R7.0.10/base/include/epicsThread.h:151:30: note: declared here
  151 | LIBCOM_API void epicsStdCall epicsThreadExitMain(void) EPICS_DEPRECATED;
      |                              ^~~~~~~~~~~~~~~~~~~

Related to this: epics-base/epics-base#93

Looks like this file is modified version of softMain.cpp in base: https://github.com/epics-base/epics-base/blob/7.0/modules/database/src/std/softIoc/softMain.cpp . That file in base has changed a decent amount since 2018 but I think the fix would be the same as here: epics-base/epics-base@de3cdce . We could also update this file to match the newer version in base.