When transferring boolean data over the ABI, keep them as boolean types, not integer

Replace the type of all boolean variables around the ABI by NG_BOOL.
NG_BOOL is typedefed to _Bool, when compiling shared ngspice. When
sharedspice.h is use externally NG_BOOL is typdefed to bool

src/include/ngspice/sharedspice.h

@@ -87,7 +87,8 @@ ngspice.dll should never call exit() directly, but handle either the 'quit'
 request to the caller or an request for exiting upon error,
 done by callback function ngexit().
 
-All boolean signals (NG_BOOL) are of type int.
+All boolean signals (NG_BOOL) are of type _Bool, if ngspice is compiled. They
+are of type bool if sharedspice.h is used externally.
 */
 
 #ifndef NGSPICE_PACKAGE_VERSION
@@ -134,8 +135,15 @@ struct ngcomplex {
 typedef struct ngcomplex ngcomplex_t;
 #endif
 
-/* ngspice traditionally treats a boolean var as int */
-typedef int NG_BOOL;
+/* NG_BOOL is the boolean variable at the ngspice interface.
+   When ompiling ngspice shared module, typedef to _BOOL, which is boolean in C,
+   when used externally, keep it to be of type bool,
+   as has been available in the past. */
+#ifndef SHARED_MODULE
+typedef bool NG_BOOL;
+#else
+typedef _Bool NG_BOOL;
+#endif
 
 /* vector info obtained from any vector in ngspice.dll.
    Allows direct access to the ngspice internal vector structure,

src/sharedspice.c

@@ -378,8 +378,8 @@ static bool nobgtrwanted = FALSE;
 static bool wantvdat = FALSE;
 static bool wantidat = FALSE;
 static bool wantsync = FALSE;
-static bool immediate = FALSE;
-static bool coquit = FALSE;
+static NG_BOOL immediate = FALSE;
+static NG_BOOL coquit = FALSE;
 static jmp_buf errbufm, errbufc;
 static int intermj = 1;
 #ifdef XSPICE
@@ -452,7 +452,7 @@ SIMinit(IFfrontEnd* frontEnd, IFsimulator** simulator)
 static threadId_t tid, printtid, tid2;
 
 static bool fl_running = FALSE;
-static bool fl_exited = TRUE;
+static NG_BOOL fl_exited = TRUE;
 
 static bool printstopp = FALSE;
 static bool ps_exited = TRUE;
@@ -776,7 +776,7 @@ read_initialisation_file(const char *dir, const char *name)
 
 /* Checks if ngspice is running in the background */
 IMPEXP
-bool
+NG_BOOL
 ngSpice_running (void)
 {
     return (fl_running && !fl_exited);
@@ -1231,7 +1231,7 @@ static int bkpttmpsize = 0;
 
 /* set a breakpoint in ngspice */
 IMPEXP
-bool ngSpice_SetBkpt(double time)
+NG_BOOL ngSpice_SetBkpt(double time)
 {
     int error;
     CKTcircuit *ckt = NULL;