bpf-headers: ship a modified version of stdarg.h from musl to fix ebpf build on glibc

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/kernel/bpf-headers/Makefile

@@ -106,6 +106,9 @@ define Build/InstallDev
 		$(PKG_BUILD_DIR)/scripts \
 		$(PKG_BUILD_DIR)/user_headers \
 		$(1)/bpf-headers
+	$(CP) \
+		$(CURDIR)/files/stdarg.h \
+		$(1)/bpf-headers/include
 endef
 
 $(eval $(call BuildPackage,bpf-headers))

package/kernel/bpf-headers/files/stdarg.h

+#ifndef _STDARG_H
+#define _STDARG_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef __builtin_va_list va_list;
+
+#define va_start(v,l)   __builtin_va_start(v,l)
+#define va_end(v)       __builtin_va_end(v)
+#define va_arg(v,l)     __builtin_va_arg(v,l)
+#define va_copy(d,s)    __builtin_va_copy(d,s)
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif