Is the minimum libpng version calculation correct or incorrect?

### Game or games this happens in

None

### What area of the game / PPSSPP

My intuition from 15 years of regularly using GNU/Linux makes me suspect that your app's `CMakeLists.txt`'s calculation for the minimum required version of libpng is incorrect and is failing to handle my edge case correctly.

https://github.com/hrydgard/ppsspp/blob/2e528818487e4ff5764161fb1d84fbdd4305a8e0/CMakeLists.txt#L847-L852

### What should happen

libpng 1.6 should work on 64-bit Arch Linux ARM without errors occurring and without having to patch the `CMakeLists.txt` file of PPSSPP

### Logs

#### Actual behavior

```
-- Could NOT find PNG: Found unsuitable version "1.6.58", but required is at least "1.7" (found /usr/lib/libpng.so)
```

#### Expected behavior

```
-- Found PNG: /usr/lib/libpng.so (found suitable version "1.6.58", minimum required is "1.6")
```

#### Reproduction code for expected behavior

```diff
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -845,7 +845,7 @@ else()
 endif()
 
 # Arm platforms require at least libpng17.
-if(ANDROID OR ARMV7 OR ARM64 OR ARM OR IOS)
+if(ANDROID OR IOS)
     set(PNG_REQUIRED_VERSION 1.7)
 else()
     set(PNG_REQUIRED_VERSION 1.6)
````

### Platform

Linux / BSD

### Mobile device model or graphics card (GPU)

Qualcomm Adreno X1-45

### PPSSPP version affected

v1.20.4-1186-g2e52881848

### Last working version

v1.9.3-428-g2a0a64e0e

### Graphics backend (3D API)

OpenGL / GLES

### Checklist

- [x] Test in the [latest git build](https://www.ppsspp.org/devbuilds) in case it's already fixed.
- [x] [Search for other reports](https://github.com/hrydgard/ppsspp/search?q=my+issue&type=issues) of the same issue.
- [x] Try resetting settings or older versions and include if the issue is related.
- [x] Try without any cheats and without loading any save states.
- [x] Include logs or screenshots of issue.

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