Add configure check for strtoll and strtoull.

Define these to _strtoi64 and _strtoui64 if these are available instead.
diff --git a/configure.ac b/configure.ac
index 4ccc1db..5d06e6f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1328,6 +1328,8 @@
 	_strdup \
 	_stricmp \
 	_strnicmp \
+	_strtoi64 \
+	_strtoui64 \
 	_vsnprintf \
 	asctime_r \
 	chsize \
@@ -1379,6 +1381,8 @@
 	strerror \
 	strncasecmp \
 	strtold \
+	strtoll \
+	strtoull \
 	tcgetattr \
 	thr_kill2 \
 	timegm \