Add release-mode triplet for x64-linux

Building debug symbols causes CI to fail due to a lack of space.

Unfortunately, this workaround is still needed:
microsoft/vcpkg#10683

.github/workflows/build.yml

@@ -37,7 +37,7 @@ jobs:
       ARTIFACT_BASE_NAME: 'mixxx-${{ matrix.triplet }}'
       VCPKG_DEFAULT_TRIPLET: '${{ matrix.triplet }}'
       VCPKG_DEFAULT_HOST_TRIPLET: '${{ matrix.host_triplet }}'
-      VCPKG_OVERLAY_TRIPLETS: vcpkg/overlay/triplets
+      VCPKG_OVERLAY_TRIPLETS: overlay/triplets:vcpkg/overlay/triplets
       VCPKG_OVERLAY_PORTS: '${{ matrix.overlay_ports }}'
       VCPKG_ROOT: ${{ github.workspace }}/vcpkg
       MIXXX_ROOT: ${{ github.workspace }}/mixxx

overlay/triplets/x64-linux.cmake

@@ -0,0 +1,7 @@
+set(VCPKG_TARGET_ARCHITECTURE x64)
+set(VCPKG_CRT_LINKAGE dynamic)
+set(VCPKG_LIBRARY_LINKAGE static)
+
+set(VCPKG_CMAKE_SYSTEM_NAME Linux)
+
+set(VCPKG_BUILD_TYPE release)

vars/vcpkg.sh

@@ -4,5 +4,5 @@ if [ -z "$VCPKG_ROOT" ]; then
   export VCPKG_ROOT="$rootdir/vcpkg"
 fi
 
-export VCPKG_OVERLAY_TRIPLETS="$VCPKG_ROOT/overlay/triplets"
+export VCPKG_OVERLAY_TRIPLETS="$rootdir/overlay/triplets:$VCPKG_ROOT/overlay/triplets"
 export VCPKG_OVERLAY_PORTS="$VCPKG_ROOT/overlay/osx:$VCPKG_ROOT/overlay/ports"