add linux-aarch64 build

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: warmenhoven

.gitlab-ci.yml

@@ -146,6 +146,12 @@ libretro-build-linux-i686:
     - .libretro-linux-cmake-x86
     - .core-defs-linux
 
+# Linux 64-bit (ARM)
+libretro-build-linux-aarch64:
+  extends:
+    - .libretro-linux-cmake-aarch64
+    - .core-defs-linux
+
 # MacOS 32-bit
 libretro-build-osx-x86:
   extends: