fixup: configure.ac: fix: do not define HAVE_NEON unconditionally

Instead of removing AC_DEFINE(), I should have used AS_IF().

Change-Id: I20e256bd6fdb0256c95ab7073e07b7437af6a12f
Fixes: I761a7afaeda9d232ac26edff47949e911f8f1f0c
diff --git a/configure.ac b/configure.ac
index c062e5f..32ea7ca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -424,6 +424,9 @@
 		[Enable ARM NEON instructions support [default=no]]
 	)],
 	[neon=$enableval], [neon="no"])
+AS_IF([test "x$neon" = "xyes"], [
+	AC_DEFINE([HAVE_NEON],, [Support ARM NEON instructions])
+])
 AC_MSG_CHECKING([whether to enable ARM NEON instructions support])
 AC_MSG_RESULT([$neon])
 AM_CONDITIONAL(HAVE_NEON, [test "x$neon" != "xno"])