Includes headers needed for getpid()
Closes: https://bugs.gentoo.org/975955

--- a/src/core/debugger.cpp
+++ b/src/core/debugger.cpp
@@ -12,6 +12,8 @@
 #elif defined(__linux__)
 #include <filesystem>
 #include <fstream>
+#include <sys/types.h>
+#include <unistd.h>
 #elif defined(__APPLE__)
 #include <errno.h>
 #include <signal.h>