Makefile: Do not generate files if "configure" has not been run yet

When doing a "make -j10" in the vanilla QEMU source tree (without
running "configure" first), the Makefile currently generates two
files already, qemu-version.h and qemu-options.def. This should not
happen, so let's only build the generated files if config-host.mak
is available (i.e. "configure" has been run already).
Signed-off-by: NThomas Huth <thuth@redhat.com>
Message-Id: <1496926799-13040-1-git-send-email-thuth@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -791,9 +791,11 @@ endif # CONFIG_WIN
 
 # Add a dependency on the generated files, so that they are always
 # rebuilt before other object files
+ifneq ($(wildcard config-host.mak),)
 ifneq ($(filter-out $(UNCHECKED_GOALS),$(MAKECMDGOALS)),$(if $(MAKECMDGOALS),,fail))
 Makefile: $(GENERATED_FILES)
 endif
+endif
 
 .SECONDARY: $(TRACE_HEADERS) $(TRACE_HEADERS:%=%-timestamp) \
 	$(TRACE_SOURCES) $(TRACE_SOURCES:%=%-timestamp) \