Add missing includes uncovered by libc++ change

These files were previously relying on a transitive include in libc++,
which is now gone.

Bug: 325103513
Change-Id: Ibdae710e02368efe8285100ee4c395491ddc9a2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5295498
Commit-Queue: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Auto-Submit: Hans Wennborg <hans@chromium.org>
Owners-Override: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1260415}
NOKEYCHECK=True
GitOrigin-RevId: 47aeebfd83b7658ab948ea709e9ef2f82fa236ca
diff --git a/fontconfig/fontconfig_util_linux.cc b/fontconfig/fontconfig_util_linux.cc
index de42c98..289f566 100644
--- a/fontconfig/fontconfig_util_linux.cc
+++ b/fontconfig/fontconfig_util_linux.cc
@@ -10,6 +10,7 @@
 
 #include <cassert>
 #include <climits>
+#include <cstdlib>
 #include <string>
 
 namespace test_fonts {