sharedspice.c, introduce csh variable "sharedmode"

to reflect whether running as shared library

src/sharedspice.c

@@ -583,6 +583,10 @@ ngSpice_Init(SendChar* printfcn, SendStat* statusfcn, ControlledExit* ngspiceexi
     srand((unsigned int) getpid());
     TausSeed();
 
+    /* set a boolean variable to be used in .control sections */
+    bool sm = TRUE;
+    cp_vset("sharedmode", CP_BOOL, &sm);
+
     /*parameter fetcher, used in show, alter, altermod */
     if_getparam = spif_getparam_special;