Issue with having multiple analogWrite's in 1.8.1

The following code does compile, however does not output a PWM signal in 1.8.1
```c
long PosX = 0;
long TargetX = 0;

void setup() {
Serial.begin(115200);
analogWrite(9, 0);
}

void loop() {
if(PosX != TargetX) {
analogWrite(9,200);
} else {
analogWrite(9,200);
}
}
```
The following does output a PWM signal in 1.8.1:
```c
long PosX = 0;
long TargetX = 0;

void setup() {
Serial.begin(115200);
analogWrite(9, 0);
}

void loop() {
if(PosX != TargetX) {
//analogWrite(9,200);
} else {
analogWrite(9,200);
}
}
```
This issue does not exist in 1.6.23, where both examples output a PWM signal.

Start by reproducing the two supplied sketches with Arduino AVR core 1.8.1 and 1.6.23, comparing whether pin 9 emits PWM. Trace the analogWrite path responsible for the differing behavior between the examples. Done means both examples produce the expected PWM signal under 1.8.1 without regressing the 1.6.23 behavior.

Written by the indexing model from the issue text.