add linux-aarch64 build (#812)

this is untested on the libretro CI. Documentation is sparse on how to actually test these changes. If anyone could provide details on that process please do.

.gitlab-ci.yml

@@ -24,6 +24,10 @@ include:
   - project: 'libretro-infrastructure/ci-templates'
     file: '/linux-x64.yml'
 
+  # Linux 64-bit (ARM64)
+  - project: 'libretro-infrastructure/ci-templates'
+    file: '/linux-aarch64.yml'
+
   # Linux 32-bit
   - project: 'libretro-infrastructure/ci-templates'
     file: '/linux-i686.yml'
@@ -92,6 +96,17 @@ libretro-build-linux-x64:
     HAVE_PARALLEL: 1
     HAVE_PARALLEL_RSP: 1
 
+# Linux 64-bit (ARM64)
+libretro-build-linux-aarch64:
+  extends:
+    - .core-defs
+    - .libretro-linux-aarch64-make-default
+  variables:
+    WITH_DYNAREC: aarch64
+    HAVE_THR_AL: 1
+    HAVE_PARALLEL: 1
+    HAVE_PARALLEL_RSP: 1
+
 # Linux 32-bit
 libretro-build-linux-i686:
   extends: