fs/Limits: convert macro to "constexpr"

src/PlaylistFile.cxx

@@ -384,7 +384,7 @@ spl_append_song(const char *utf8path, Song *song, Error &error)
 		return false;
 	}
 
-	if (st.st_size / (MPD_PATH_MAX + 1) >= (off_t)playlist_max_length) {
+	if (st.st_size / off_t(MPD_PATH_MAX + 1) >= (off_t)playlist_max_length) {
 		fclose(file);
 		error.Set(playlist_domain, PLAYLIST_RESULT_TOO_LARGE,
 			  "Stored playlist is too large");

src/fs/FileSystem.cxx

@@ -34,7 +34,7 @@ Path ReadLink(const Path &path)
 	ssize_t size = readlink(path.c_str(), buffer, MPD_PATH_MAX);
 	if (size < 0)
 		return Path::Null();
-	if (size >= MPD_PATH_MAX) {
+	if (size_t(size) >= MPD_PATH_MAX) {
 		errno = ENOMEM;
 		return Path::Null();
 	}

src/fs/Limits.hxx

@@ -22,18 +22,17 @@
 
 #include "check.h"
 
+#include <stddef.h>
 #include <limits.h>
 
-#if !defined(MPD_PATH_MAX)
-#  if defined(WIN32)
-#    define MPD_PATH_MAX 260
-#  elif defined(MAXPATHLEN)
-#    define MPD_PATH_MAX MAXPATHLEN
-#  elif defined(PATH_MAX)
-#    define MPD_PATH_MAX PATH_MAX
-#  else
-#    define MPD_PATH_MAX 256
-#  endif
+#if defined(WIN32)
+static constexpr size_t MPD_PATH_MAX = 260;
+#elif defined(MAXPATHLEN)
+static constexpr size_t MPD_PATH_MAX = MAXPATHLEN;
+#elif defined(PATH_MAX)
+static constexpr size_t MPD_PATH_MAX = PATH_MAX;
+#else
+static constexpr size_t MPD_PATH_MAX = 256;
 #endif
 
 #endif

src/fs/Path.cxx

@@ -45,7 +45,7 @@
  * and assumption that some weird encoding could represent some UTF-8 4 byte
  * sequences with single byte.
  */
-#define MPD_PATH_MAX_UTF8 ((MPD_PATH_MAX - 1) * 4 + 1)
+static constexpr size_t MPD_PATH_MAX_UTF8 = (MPD_PATH_MAX - 1) * 4 + 1;
 
 const Domain path_domain("path");