LibCore: Implement FileWatcher for any systems with inotify

FreeBSD 15 added support for inotify so let's just allow this file to
be used there too as it's needed for watching the time zone file.

Libraries/LibCore/CMakeLists.txt

@@ -80,28 +80,34 @@ else()
     list(APPEND SOURCES LocalServerWindows.cpp)
 endif()
 
-# FIXME: Implement these for other systems.
+include(CheckIncludeFile)
+
+check_include_file(sys/inotify.h HAVE_INOTIFY)
+
+if (HAVE_INOTIFY)
+    list(APPEND SOURCES FileWatcherInotify.cpp)
+else()
+    list(APPEND SOURCES FileWatcherUnimplemented.cpp)
+endif()
+
+# FIXME: Implement ProcessStatistics for Windows and *BSD
 if (LINUX)
     list(APPEND SOURCES
-        FileWatcherLinux.cpp
         Platform/ProcessStatisticsLinux.cpp
         TimeZoneWatcherLinux.cpp
     )
 elseif (APPLE AND NOT IOS)
     list(APPEND SOURCES
-        FileWatcherUnimplemented.cpp
         Platform/ProcessStatisticsMach.cpp
         TimeZoneWatcherMacOS.mm
     )
 elseif (WIN32)
     list(APPEND SOURCES
-        FileWatcherUnimplemented.cpp
         Platform/ProcessStatisticsUnimplemented.cpp
         TimeZoneWatcherWindows.cpp
     )
 else()
     list(APPEND SOURCES
-        FileWatcherUnimplemented.cpp
         Platform/ProcessStatisticsUnimplemented.cpp
         TimeZoneWatcherUnimplemented.cpp
     )

Libraries/LibCore/FileWatcherInotify.cpp

@@ -16,10 +16,6 @@
 #include <sys/ioctl.h>
 #include <unistd.h>
 
-#if !defined(AK_OS_LINUX)
-static_assert(false, "This file must only be used for Linux");
-#endif
-
 namespace Core {
 
 static constexpr unsigned file_watcher_flags_to_inotify_flags(FileWatcherFlags flags)