libfido2: Fix build for Linuxbrew

We introduced libfido2 in Homebrew/homebrew-core#50326, but it has different dependencies on Linux.

Additionally, the upstream CMake code uses share/man/ on Linux but man/ on macOS.

Formula/libfido2.rb

@@ -15,6 +15,8 @@ class Libfido2 < Formula
   depends_on "pkg-config" => :build
   depends_on "libcbor"
   depends_on "[email protected]"
+
+  depends_on "systemd" if OS.linux? # libfido2 uses libudev on Linux but IOKit on macOS
 
   def install
     mkdir "build" do
@@ -24,7 +26,7 @@ def install
       system "make", "man_symlink"
       system "make", "install"
     end
-    mv prefix/"man", share/"man"
+    mv prefix/"man", share/"man" if OS.mac? # Path bug on macOS might be upstream
   end
 
   test do