audioreactive: Move flags to library

Use a PlatformIO script to move the last of AR_buildflags in to the
module itself.

usermods/audioreactive/library.json

@@ -1,17 +1,16 @@
-{
-  "name": "audioreactive",
-  "build": {
-    "srcDir": ".",
-    "includeDir": "../../wled00",
-    "libLDFMode": "chain+",
-    "libArchive": false
-  },
-  "dependencies": [
-    {
-      "owner": "kosme",      
-      "name": "arduinoFFT",
-      "version": "2.0.1",
-      "platforms": "espressif32"
-    }
-  ]
+{
+  "name": "audioreactive",
+  "build": {
+    "srcDir": ".",
+    "includeDir": "../../wled00",
+    "extraScript": "override_sqrt.py"
+  },
+  "dependencies": [
+    {
+      "owner": "kosme",      
+      "name": "arduinoFFT",
+      "version": "2.0.1",
+      "platforms": "espressif32"
+    }
+  ]
 }

usermods/audioreactive/override_sqrt.py

@@ -0,0 +1,5 @@
+Import('env')
+
+for lb in env.GetLibBuilders():
+    if lb.name == "arduinoFFT":
+        lb.env.Append(CPPDEFINES=[("sqrt_internal", "sqrtf")])