fix: some const for g++ compiler in fastmath

fastmath.hpp

@@ -161,7 +161,7 @@ template <int n, class Dev> struct vec {
     }
 
     friend decimal operator*(const vec<n, Dev> &v1, const vec<n, Dev> &v2) {
-        decimal res = {0};
+        decimal res = decimal(0.0f);
         for (int i = 0; i < n; i++) {
             res += v1.v[i] * v2.v[i];
         }
@@ -242,7 +242,6 @@ struct vec4 : public vec<4, vec4> {
     vec4(int32_t x, int32_t y, int32_t z, int32_t w)
         : vec<4, vec4>(decimal(x), decimal(y), decimal(z), decimal(w)) {}
 
-    vec4(decimal x, decimal y, decimal z) : vec<4, vec4>(x, y, z, 0) {}
 
     decimal &x() { return v[0]; }
     decimal &y() { return v[1]; }