diff -Naur gzdoom-g1.8.09/game-music-emu/CMakeLists.txt gzdoom-g1.8.09.patched/game-music-emu/CMakeLists.txt
--- gzdoom-g1.8.09/game-music-emu/CMakeLists.txt	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/game-music-emu/CMakeLists.txt	2021-10-09 16:57:46.630159506 -0400
@@ -84,7 +84,7 @@
    if (__LIBGME_TEST_VISIBILITY)
       # get the gcc version
       exec_program(${CMAKE_CXX_COMPILER} ARGS --version OUTPUT_VARIABLE _gcc_version_info)
-      string (REGEX MATCH "[3-9]\\.[0-9]\\.[0-9]" _gcc_version "${_gcc_version_info}")
+      string (REGEX MATCH "[1-9][0-9]*\\.[0-9]\\.[0-9]" _gcc_version "${_gcc_version_info}")
 
       # gcc <4.1 had poor support for symbol visibility
       if ((${_gcc_version} VERSION_GREATER "4.1") OR (${_gcc_version} VERSION_EQUAL "4.1"))
diff -Naur gzdoom-g1.8.09/src/b_func.cpp gzdoom-g1.8.09.patched/src/b_func.cpp
--- gzdoom-g1.8.09/src/b_func.cpp	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/src/b_func.cpp	2021-10-09 16:57:46.631159506 -0400
@@ -123,7 +123,7 @@
 	if (vangle == 0)
 		return false; //Looker seems to be blind.
 
-	return (angle_t)abs (R_PointToAngle2 (player->mo->x, player->mo->y, to->x, to->y) - player->mo->angle) <= vangle/2;
+	return (angle_t)fabs (R_PointToAngle2 (player->mo->x, player->mo->y, to->x, to->y) - player->mo->angle) <= vangle/2;
 }
 
 //-------------------------------------
@@ -210,7 +210,7 @@
 			{
 				angle = an;
 				//have to be somewhat precise. to avoid suicide.
-				if (abs (angle - player->mo->angle) < 12*ANGLE_1)
+				if (fabs (angle - player->mo->angle) < 12*ANGLE_1)
 				{
 					t_rocket = 9;
 					no_fire = false;
@@ -252,7 +252,7 @@
 				angle -= m;
 		}
 
-		if (abs (angle - player->mo->angle) < 4*ANGLE_1)
+		if (fabs (angle - player->mo->angle) < 4*ANGLE_1)
 		{
 			increase = !increase;
 		}
diff -Naur gzdoom-g1.8.09/src/g_hexen/a_dragon.cpp gzdoom-g1.8.09.patched/src/g_hexen/a_dragon.cpp
--- gzdoom-g1.8.09/src/g_hexen/a_dragon.cpp	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/src/g_hexen/a_dragon.cpp	2021-10-09 17:06:47.628110327 -0400
@@ -79,7 +79,7 @@
 	{ // attack the destination mobj if it's attackable
 		AActor *oldTarget;
 	
-		if (abs(actor->angle-R_PointToAngle2(actor->x, actor->y, 
+		if (fabs(actor->angle-R_PointToAngle2(actor->x, actor->y, 
 			target->x, target->y)) < ANGLE_45/2)
 		{
 			oldTarget = actor->target;
@@ -121,9 +121,9 @@
 				}
 				angleToSpot = R_PointToAngle2(actor->x, actor->y, 
 					mo->x, mo->y);
-				if ((angle_t)abs(angleToSpot-angleToTarget) < bestAngle)
+				if ((angle_t)fabs(angleToSpot-angleToTarget) < bestAngle)
 				{
-					bestAngle = abs(angleToSpot-angleToTarget);
+					bestAngle = fabs(angleToSpot-angleToTarget);
 					bestActor = mo;
 				}
 			}
@@ -198,14 +198,14 @@
 		}
 		angle = R_PointToAngle2(self->x, self->y, self->target->x,
 			self->target->y);
-		if (abs(self->angle-angle) < ANGLE_45/2 && self->CheckMeleeRange())
+		if (fabs(self->angle-angle) < ANGLE_45/2 && self->CheckMeleeRange())
 		{
 			int damage = pr_dragonflight.HitDice (8);
 			int newdam = P_DamageMobj (self->target, self, self, damage, NAME_Melee);
 			P_TraceBleed (newdam > 0 ? newdam : damage, self->target, self);
 			S_Sound (self, CHAN_WEAPON, self->AttackSound, 1, ATTN_NORM);
 		}
-		else if (abs(self->angle-angle) <= ANGLE_1*20)
+		else if (fabs(self->angle-angle) <= ANGLE_1*20)
 		{
 			self->SetState (self->MissileState);
 			S_Sound (self, CHAN_WEAPON, self->AttackSound, 1, ATTN_NORM);
diff -Naur gzdoom-g1.8.09/src/g_hexen/a_heresiarch.cpp gzdoom-g1.8.09.patched/src/g_hexen/a_heresiarch.cpp
--- gzdoom-g1.8.09/src/g_hexen/a_heresiarch.cpp	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/src/g_hexen/a_heresiarch.cpp	2021-10-09 17:06:55.063109651 -0400
@@ -314,7 +314,7 @@
 	case SORC_STOPPING:			// Balls stopping
 		if ((parent->StopBall == RUNTIME_TYPE(actor)) &&
 			 (parent->args[1] > SORCBALL_SPEED_ROTATIONS) &&
-			 (abs(angle - (parent->angle>>ANGLETOFINESHIFT)) < (30<<5)))
+			 (fabs(angle - (parent->angle>>ANGLETOFINESHIFT)) < (30<<5)))
 		{
 			// Can stop now
 			actor->target->args[3] = SORC_FIRESPELL;
diff -Naur gzdoom-g1.8.09/src/g_hexen/a_hexenspecialdecs.cpp gzdoom-g1.8.09.patched/src/g_hexen/a_hexenspecialdecs.cpp
--- gzdoom-g1.8.09/src/g_hexen/a_hexenspecialdecs.cpp	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/src/g_hexen/a_hexenspecialdecs.cpp	2021-10-09 17:07:05.703108684 -0400
@@ -109,7 +109,7 @@
 		if (playeringame[i])
 		{
 			AActor *pmo = players[i].mo;
-			if (P_CheckSight (self, pmo) && (abs (R_PointToAngle2 (pmo->x,
+			if (P_CheckSight (self, pmo) && (fabs (R_PointToAngle2 (pmo->x,
 				pmo->y, self->x, self->y) - pmo->angle) <= ANGLE_45))
 			{ // Previous state (pottery bit waiting state)
 				self->SetState (self->state - 1);
diff -Naur gzdoom-g1.8.09/src/p_enemy.cpp gzdoom-g1.8.09.patched/src/p_enemy.cpp
--- gzdoom-g1.8.09/src/p_enemy.cpp	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/src/p_enemy.cpp	2021-10-09 16:57:46.631159506 -0400
@@ -2738,7 +2738,7 @@
 
 	// 0 means no limit. Also, if we turn in a single step anyways, no need to go through the algorithms.
 	// It also means that there is no need to check for going past the other.
-	if (max_turn && (max_turn < (angle_t)abs(self->angle - other_angle)))
+	if (max_turn && (max_turn < (angle_t)fabs(self->angle - other_angle)))
 	{
 		if (self->angle > other_angle)
 		{
diff -Naur gzdoom-g1.8.09/src/p_mobj.cpp gzdoom-g1.8.09.patched/src/p_mobj.cpp
--- gzdoom-g1.8.09/src/p_mobj.cpp	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/src/p_mobj.cpp	2021-10-09 16:59:08.847152032 -0400
@@ -2932,7 +2932,7 @@
 	if (thing->flags4&MF4_SHIELDREFLECT)
 	{
 		// Shield reflection (from the Centaur
-		if (abs (angle - thing->angle)>>24 > 45)
+		if ((int)(fabs (angle - thing->angle))>>24 > 45)
 			return true;	// Let missile explode
 
 		if (thing->IsKindOf (RUNTIME_CLASS(AHolySpirit)))	// shouldn't this be handled by another flag???
diff -Naur gzdoom-g1.8.09/src/p_setup.cpp gzdoom-g1.8.09.patched/src/p_setup.cpp
--- gzdoom-g1.8.09/src/p_setup.cpp	2014-12-21 09:18:40.000000000 -0500
+++ gzdoom-g1.8.09.patched/src/p_setup.cpp	2021-10-09 17:02:30.783133675 -0400
@@ -1311,7 +1311,7 @@
 
 			ptp_angle = R_PointToAngle2 (li->v1->x, li->v1->y, li->v2->x, li->v2->y);
 			dis = 0;
-			delta_angle = (abs(ptp_angle-(segangle<<16))>>ANGLETOFINESHIFT)*360/FINEANGLES;
+			delta_angle = ((int)fabs(ptp_angle-(segangle<<16))>>ANGLETOFINESHIFT)*360/FINEANGLES;
 
 			if (delta_angle != 0)
 			{