libpkgconf: path: use realpath(3) to deduplicate the search path

closes #24

NEWS

@@ -10,6 +10,8 @@ Changes from 1.6.0 to 1.6.1:
   - Fixed a regression where having an empty PKG_CONFIG_LIBDIR
     environment variable would not eliminate the default search
     paths.
+  - Use POSIX realpath(3) instead of readlink() for deduplicating the
+    search path.  Use _fullpath() on Windows for the same purpose.
 
 Changes from 1.5.4 to 1.6.0:
 ----------------------------

libpkgconf/libpkgconf.h

@@ -41,6 +41,10 @@ extern "C" {
 #define PKG_DIR_SEP_S   '/'
 #endif
 
+#ifdef _WIN32
+#define realpath(N,R) _fullpath((R),(N),_MAX_PATH)
+#endif
+
 #define PKGCONF_BUFSIZE	(65535)
 
 typedef enum {

libpkgconf/path.c

@@ -92,14 +92,9 @@ pkgconf_path_add(const char *text, pkgconf_list_t *dirlist, bool filter)
 			return;
 		if (S_ISLNK(st.st_mode))
 		{
-			char linkdest[PKGCONF_ITEM_SIZE];
-			ssize_t len;
+			char *linkdest = realpath(path, NULL);
 
-			memset(linkdest, '\0', sizeof linkdest);
-			len = readlink(path, linkdest, sizeof linkdest);
-
-			if (len != -1 && (size_t)len < sizeof(linkdest) &&
-				stat(linkdest, &st) == -1)
+			if (linkdest != NULL && stat(linkdest, &st) == -1)
 				return;
 		}
 		if (path_list_contains_entry(path, dirlist, &st))