compositor: add fallback strchrnul()

Android does not have this function.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/shared/os-compatibility.c b/shared/os-compatibility.c
index 66934a8..21d4d02 100644
--- a/shared/os-compatibility.c
+++ b/shared/os-compatibility.c
@@ -168,3 +168,13 @@
 
 	return fd;
 }
+
+#ifndef HAVE_STRCHRNUL
+char *
+strchrnul(const char *s, int c)
+{
+	while (*s && *s != c)
+		s++;
+	return (char *)s;
+}
+#endif