chore: Move PGO builds for macos behind a pref, b=no-bug, c=configs

Author: mr-cheffy

configs/macos/mozconfig

@@ -12,11 +12,13 @@ ac_add_options --enable-eme=widevine
 export MOZ_LTO=cross,thin
 ac_add_options --enable-lto=cross,thin
 
-if test "$ZEN_GA_DISABLE_PGO"; then
-  export ZEN_DUMMY=1
-else
-  export MOZ_PGO=1
-  ac_add_options MOZ_PGO=1
+if test "$ZEN_RELEASE"; then
+  if test "$ZEN_GA_DISABLE_PGO"; then
+    export ZEN_DUMMY=1
+  else
+    export MOZ_PGO=1
+    ac_add_options MOZ_PGO=1
+  fi
 fi
 
 if test "$SURFER_COMPAT" = "x86_64"; then