Added configure check for spawnvp().

diff --git a/configure.ac b/configure.ac
index 11b597e..98fcece 100644
--- a/configure.ac
+++ b/configure.ac
@@ -971,6 +971,7 @@
 	settimeofday \
 	sigaltstack \
 	snprintf \
+	spawnvp \
 	statfs \
 	strcasecmp \
 	strerror \