diff -rupN grass-7.8.5/vector/v.hull/chull.c grass-7.8.5-new/vector/v.hull/chull.c
--- grass-7.8.5/vector/v.hull/chull.c	2020-12-21 19:40:15.000000000 +0100
+++ grass-7.8.5-new/vector/v.hull/chull.c	2021-05-10 10:56:36.399167493 +0200
@@ -31,7 +31,7 @@
 
 /*Define Boolean type */
 typedef enum
-{ BFALSE, BTRUE } bool;
+{ BFALSE, BTRUE } grass_bool;
 
 /* Define vertex indices. */
 #define X   0
@@ -53,8 +53,8 @@ struct tVertexStructure
     double v[3];
     int vnum;
     tEdge duplicate;		/* pointer to incident cone edge (or NULL) */
-    bool onhull;		/* T iff point on hull. */
-    bool mark;			/* T iff point already processed. */
+    grass_bool onhull;		/* T iff point on hull. */
+    grass_bool mark;			/* T iff point already processed. */
     tVertex next, prev;
 };
 
@@ -63,7 +63,7 @@ struct tEdgeStructure
     tFace adjface[2];
     tVertex endpts[2];
     tFace newface;		/* pointer to incident cone face. */
-    bool delete;		/* T iff edge should be delete. */
+    grass_bool delete;		/* T iff edge should be delete. */
     tEdge next, prev;
 };
 
@@ -71,7 +71,7 @@ struct tFaceStructure
 {
     tEdge edge[3];
     tVertex vertex[3];
-    bool visible;		/* T iff face visible from new point. */
+    grass_bool visible;		/* T iff face visible from new point. */
     tFace next, prev;
 };
 
@@ -92,7 +92,7 @@ void ReadVertices(double *px, double *py
 void writeVertices(struct Map_info *Map);
 int DoubleTriangle(void);
 void ConstructHull(void);
-bool AddOne(tVertex p);
+grass_bool AddOne(tVertex p);
 int VolumeSign(tFace f, tVertex p);
 tFace MakeConeFace(tEdge e, tVertex p);
 void MakeCcw(tFace f, tEdge e, tVertex p);
@@ -103,7 +103,7 @@ void CleanUp(void);
 void CleanEdges(void);
 void CleanFaces(void);
 void CleanVertices(void);
-bool Collinear(tVertex a, tVertex b, tVertex c);
+grass_bool Collinear(tVertex a, tVertex b, tVertex c);
 
 #include "macros.h"
 
@@ -388,7 +388,7 @@ vertices are those in the list marked as
 void ConstructHull(void)
 {
     tVertex v, vnext;
-    bool changed;		/* T if addition changes hull; not used. */
+    grass_bool changed;		/* T if addition changes hull; not used. */
     int i;
     int numVertices;
 
@@ -431,12 +431,12 @@ onhull.  Next is a loop over edges.  If
 are visible, then the edge is marked for deletion.  If just one of the
 adjacent faces is visible then a new face is constructed.
 ---------------------------------------------------------------------*/
-bool AddOne(tVertex p)
+grass_bool AddOne(tVertex p)
 {
     tFace f;
     tEdge e, temp;
     long int vol;
-    bool vis = BFALSE;
+    grass_bool vis = BFALSE;
 
 
     /* Mark faces visible from p. */
@@ -789,7 +789,7 @@ void CleanVertices(void)
 Collinear checks to see if the three points given are collinear,
 by checking to see if each element of the cross product is zero.
 ---------------------------------------------------------------------*/
-bool Collinear(tVertex a, tVertex b, tVertex c)
+grass_bool Collinear(tVertex a, tVertex b, tVertex c)
 {
     return
 	(c->v[Z] - a->v[Z]) * (b->v[Y] - a->v[Y]) -