Added configure test for the header file <asm/unistd.h>.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@8968 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/configure.in b/configure.in
index 51671c3..d81021d 100644
--- a/configure.in
+++ b/configure.in
@@ -1269,6 +1269,7 @@
 # Checks for C header files.
 AC_HEADER_STDC
 AC_CHECK_HEADERS([       \
+        asm/unistd.h     \
         endian.h         \
         mqueue.h         \
         sys/endian.h     \