include/qemu/osdep: Add qemu_build_assert

This differs from assert, in that with optimization enabled it
triggers at build-time.  It differs from QEMU_BUILD_BUG_ON,
aka _Static_assert, in that it is sensitive to control flow
and is subject to dead-code elimination.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/qemu/osdep.h

@@ -186,6 +186,14 @@ void QEMU_ERROR("code path is reachable")
 #define qemu_build_not_reached()  g_assert_not_reached()
 #endif
 
+/**
+ * qemu_build_assert()
+ *
+ * The compiler, during optimization, is expected to prove that the
+ * assertion is true.
+ */
+#define qemu_build_assert(test)  while (!(test)) qemu_build_not_reached()
+
 /*
  * According to waitpid man page:
  * WCOREDUMP