common: Avoid errors on systems that define strnlen but not strndup

Add a configure test for a system library supplied strnlen, and disable
the embedded version in common if one is found.

Signed-off-by: Will Miles <wmiles@sgl.com>
Signed-off-by: Allan McRae <allan@archlinux.org>

configure.ac

@@ -304,8 +304,8 @@ AC_FUNC_MKTIME
 AC_FUNC_STRCOLL
 AC_CHECK_FUNCS([dup2 getcwd getmntinfo gettimeofday memmove memset \
                 mkdir realpath regcomp rmdir setenv setlocale strcasecmp \
-                strchr strcspn strdup strerror strndup strrchr strsep strstr \
-                strtol swprintf tcflush wcwidth uname])
+                strchr strcspn strdup strerror strndup strnlen strrchr \
+                strsep strstr strtol swprintf tcflush wcwidth uname])
 AC_CHECK_MEMBERS([struct stat.st_blksize],,,[[#include <sys/stat.h>]])
 
 # For the diskspace code

src/common/util-common.c

@@ -127,7 +127,7 @@ char *safe_fgets(char *s, int size, FILE *stream)
 	return ret;
 }
 
-#ifndef HAVE_STRNDUP
+#ifndef HAVE_STRNLEN
 /* A quick and dirty implementation derived from glibc */
 /** Determines the length of a fixed-size string.
  * @param s string to be measured
@@ -140,7 +140,9 @@ static size_t strnlen(const char *s, size_t max)
 	for(p = s; *p && max--; ++p);
 	return (p - s);
 }
+#endif
 
+#ifndef HAVE_STRNDUP
 /** Copies a string.
  * Returned string needs to be freed
  * @param s string to be copied