Make systemd detection more robust

We don't need to look for this on Windows or macOS, and we need to be
able to gracefully handle systems without pkg-config.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6028fadfa5d7cb051e7264bf930db0d110a52d13..f1bfd61850029fafa52c1bce2cd38b6308064fa1 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -302,7 +302,12 @@ if(UNIX AND NOT APPLE)
 endif()
 
 # check for systemd support (socket activation)
-pkg_check_modules(LIBSYSTEMD libsystemd)
+if(UNIX AND NOT APPLE)
+  find_package(PkgConfig)
+  if (PKG_CONFIG_FOUND)
+    pkg_check_modules(LIBSYSTEMD libsystemd)
+  endif()
+endif()
 
 # Generate config.h and make sure the source finds it
 configure_file(config.h.in config.h)