fix: Custom vscode triplet for MacOS devcontainer (#148)

- When running a Linux container on MacOS, the mpg123 library fails with REAL_IS_FIXED, which I think means that this distro/arch combination fails to infer it automatically. As a workaround I explicitly set HAVE_FPU. If this is OK, I can remove the FIXME comment, but it's there for now for discussion in PR.

tools/triplets/arm64-linux.cmake

@@ -0,0 +1,10 @@
+set(VCPKG_TARGET_ARCHITECTURE arm64)
+set(VCPKG_CRT_LINKAGE dynamic)
+set(VCPKG_LIBRARY_LINKAGE static)
+
+set(VCPKG_CMAKE_SYSTEM_NAME Linux)
+
+# FIXME for discussion in PR. I had to add this to get containers working in MacOS, as it seems the macro is not set correctly by default.
+if (PORT MATCHES "mpg123")
+    set(VCPKG_CMAKE_CONFIGURE_OPTIONS "-DHAVE_FPU=1")
+endif()