ANSI C fixes.

diff --git a/configure.in b/configure.in
index 516b211..7bd0ad7 100644
--- a/configure.in
+++ b/configure.in
@@ -438,6 +438,7 @@
 
 dnl **** Check for functions ****
 
+AC_FUNC_ALLOCA()
 AC_CHECK_FUNCS(\
 	_lwp_create \
 	clone \