Added a configure script to emulate GNU autoconf and related changes.

Changes included in this set:

 * Added strlcat() and strlcpy() from OpenBSD, always use them if the
   system does not have them built in.
 * Changed an array of PATH_MAX size allocated in the stack, to a dynamically
   allocated buffer from heap. This should reduce memory usage a bit.
 * Simplify code that implemented a homegrown realpath(3) implementation,
   simply use realpath(3).
 * If compiler supports -fstack-protector, build all code with
   -D_FORTIFY_SOURCE=2 and --param ssp-buffer-size=1 so that all
   buffers are protected.

lib/pkgmatch.c

@@ -26,6 +26,7 @@
 #include <fnmatch.h>
 
 #include <xbps_api.h>
+#include "config.h"
 
 /**
  * @file lib/pkgmatch.c
@@ -116,7 +117,8 @@ int
 xbps_pkgpattern_match(const char *instpkg, char *pattern)
 {
 	const char *fname = instpkg;
-	char basefname[PATH_MAX], condchar = '\0', *condition;
+	char *basefname, condchar = '\0', *condition;
+	size_t len = 0;
 	int rv = 0;
 
 	memset(&basefname, 0, sizeof(basefname));
@@ -134,7 +136,11 @@ xbps_pkgpattern_match(const char *instpkg, char *pattern)
 		*condition = '\0';
 		ch = strrchr(fname, '-');
 		if (ch && ch - fname < PATH_MAX) {
-			strncpy(basefname, fname, ch - fname);
+			len = ch - fname + 1;
+			basefname = malloc(len);
+			if (basefname == NULL)
+				return -1;
+			strlcpy(basefname, fname, len);
 			fname = basefname;
 		}
 	}
@@ -177,6 +183,8 @@ xbps_pkgpattern_match(const char *instpkg, char *pattern)
 			break;
 		}
 	}
+	if (basefname)
+		free(basefname);
 
 	return rv;
 }