patches/rules_foreign_cc_make_cppflags.patch

diff --git a/foreign_cc/built_tools/make_build.bzl b/foreign_cc/built_tools/make_build.bzl
--- a/foreign_cc/built_tools/make_build.bzl
+++ b/foreign_cc/built_tools/make_build.bzl
@@ -114,6 +114,11 @@
             "ARFLAGS": _join_flags_list(ctx.workspace_name, arflags),
             "CC": absolute_cc,
             "CFLAGS": _join_flags_list(ctx.workspace_name, non_sysroot_cflags),
+            # Configure's preprocessor checks need the declared header paths too.
+            "CPPFLAGS": " ".join([
+                "$${CPPFLAGS:-}$$",
+                _join_flags_list(ctx.workspace_name, non_sysroot_cflags),
+            ]).strip(),
             "LD": absolute_ld,
             "LDFLAGS": _join_flags_list(ctx.workspace_name, non_sysroot_ldflags),
         })