Complementary fix for rB8054372: Follow the common naming scheme by

using negate_mat3_m4 instead of negate_m4.

This avoids changing the behavior and only flips the 3x3 part of the
matrix.

source/blender/blenlib/BLI_math_matrix.h

@@ -126,6 +126,7 @@ void mul_m4_fl(float R[4][4], float f);
 void mul_mat3_m4_fl(float R[4][4], float f);
 
 void negate_m3(float R[3][3]);
+void negate_mat3_m4(float R[4][4]);
 void negate_m4(float R[4][4]);
 
 bool invert_m3_ex(float m[3][3], const float epsilon);

source/blender/blenlib/intern/math_matrix.c

@@ -648,6 +648,15 @@ void negate_m3(float m[3][3])
 			m[i][j] *= -1.0f;
 }
 
+void negate_mat3_m4(float m[4][4])
+{
+	int i, j;
+
+	for (i = 0; i < 3; i++)
+		for (j = 0; j < 3; j++)
+			m[i][j] *= -1.0f;
+}
+
 void negate_m4(float m[4][4])
 {
 	int i, j;

source/blender/editors/object/object_bake_api.c

@@ -768,7 +768,7 @@ static int bake(
 			normalize_m4_m4(highpoly[i].rotmat, highpoly[i].imat);
 			zero_v3(highpoly[i].rotmat[3]);
 			if (is_negative_m4(highpoly[i].rotmat))
-				negate_m4(highpoly[i].rotmat);
+				negate_mat3_m4(highpoly[i].rotmat);
 
 			i++;
 		}