libksysguard underlinks on musl.

--- libksysguard-5.24.5/processcore/CMakeLists.txt.old	2022-05-03 05:29:20.000000000 -0500
+++ libksysguard-5.24.5/processcore/CMakeLists.txt	2022-06-06 00:00:11.841140703 -0500
@@ -36,6 +36,7 @@
     KF5::CoreAddons
     KF5::Service
     ZLIB::ZLIB
+    stdc++fs
 )
 
 if( ${CMAKE_SYSTEM_NAME} MATCHES "NetBSD" )