profile: use specialized time__vpc_now

vlib/time/time_nix.c.v

@@ -39,3 +39,19 @@ fn sys_mono_now() u64 {
 	}
 }
 
+// NB: vpc_now is used by `v -profile` .
+// It should NOT call *any other v function*, just C functions and casts.
+[inline]
+fn vpc_now() u64 {
+	$if macos {
+		tm := C.mach_absolute_time()
+		if time_base.denom == 0 {
+			C.mach_timebase_info(&time_base)
+		}
+		return (tm - start_time) * time_base.numer / time_base.denom
+	} $else {    
+		ts := C.timespec{}
+		C.clock_gettime(C.CLOCK_MONOTONIC, &ts)
+		return u64(ts.tv_sec) * 1_000_000_000 + u64(ts.tv_nsec)
+	}
+}