add qbe config to copmile

src/qbe/config.h

@@ -0,0 +1,18 @@
+/* Auto-generated default target for QBE.
+   The qbe_backend.c #ifdef chain handles all common platforms;
+   this file is only reached by the #else fallback. */
+#if defined(__aarch64__) && defined(__APPLE__)
+#define Deftgt T_arm64_apple
+#elif defined(__aarch64__)
+#define Deftgt T_arm64
+#elif defined(__x86_64__) && defined(__APPLE__)
+#define Deftgt T_amd64_apple
+#elif defined(__x86_64__) && defined(_WIN32)
+#define Deftgt T_amd64_win
+#elif defined(__x86_64__)
+#define Deftgt T_amd64_sysv
+#elif defined(__riscv) && __riscv_xlen == 64
+#define Deftgt T_rv64
+#else
+#error "unsupported target for QBE"
+#endif