trace: rerun tracetool after ./configure changes

Autogenerated code in trace.h/trace.c and friends is specific to the
config-host.mak TRACE_BACKENDS setting and must be regenerated when
./configure --enable-trace-backend= changes settings.

This patch ensures that changes to TRACE_BACKENDS are detected.  For
example, the trace-root.h file is now updated after switching trace
backends:

  $ ./configure && make
  $ cp trace-root.h /tmp/old-trace-root.h
  $ ./configure --enable-trace-backend=simple && make
  $ diff -u /tmp/old-trace-root.h trace-root.h

Reported-by: Christophe Lyon <christophe.lyon@st.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20190129025343.4788-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Makefile

@@ -145,7 +145,7 @@ tracetool-y += $(shell find $(SRC_PATH)/scripts/tracetool -name "*.py")
 
 %/trace.h: %/trace.h-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-%/trace.h-timestamp: $(SRC_PATH)/%/trace-events $(tracetool-y)
+%/trace.h-timestamp: $(SRC_PATH)/%/trace-events $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=$(call trace-group-name,$@) \
 		--format=h \
@@ -154,7 +154,7 @@ tracetool-y += $(shell find $(SRC_PATH)/scripts/tracetool -name "*.py")
 
 %/trace.c: %/trace.c-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-%/trace.c-timestamp: $(SRC_PATH)/%/trace-events $(tracetool-y)
+%/trace.c-timestamp: $(SRC_PATH)/%/trace-events $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=$(call trace-group-name,$@) \
 		--format=c \
@@ -163,7 +163,7 @@ tracetool-y += $(shell find $(SRC_PATH)/scripts/tracetool -name "*.py")
 
 %/trace-ust.h: %/trace-ust.h-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-%/trace-ust.h-timestamp: $(SRC_PATH)/%/trace-events $(tracetool-y)
+%/trace-ust.h-timestamp: $(SRC_PATH)/%/trace-events $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=$(call trace-group-name,$@) \
 		--format=ust-events-h \
@@ -187,7 +187,7 @@ tracetool-y += $(shell find $(SRC_PATH)/scripts/tracetool -name "*.py")
 
 trace-root.h: trace-root.h-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-trace-root.h-timestamp: $(SRC_PATH)/trace-events $(tracetool-y)
+trace-root.h-timestamp: $(SRC_PATH)/trace-events $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=root \
 		--format=h \
@@ -196,7 +196,7 @@ trace-root.h-timestamp: $(SRC_PATH)/trace-events $(tracetool-y)
 
 trace-root.c: trace-root.c-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-trace-root.c-timestamp: $(SRC_PATH)/trace-events $(tracetool-y)
+trace-root.c-timestamp: $(SRC_PATH)/trace-events $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=root \
 		--format=c \
@@ -205,7 +205,7 @@ trace-root.c-timestamp: $(SRC_PATH)/trace-events $(tracetool-y)
 
 trace-ust-root.h: trace-ust-root.h-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-trace-ust-root.h-timestamp: $(SRC_PATH)/trace-events $(tracetool-y)
+trace-ust-root.h-timestamp: $(SRC_PATH)/trace-events $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=root \
 		--format=ust-events-h \
@@ -214,7 +214,7 @@ trace-ust-root.h-timestamp: $(SRC_PATH)/trace-events $(tracetool-y)
 
 trace-ust-all.h: trace-ust-all.h-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-trace-ust-all.h-timestamp: $(trace-events-files) $(tracetool-y)
+trace-ust-all.h-timestamp: $(trace-events-files) $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=all \
 		--format=ust-events-h \
@@ -223,7 +223,7 @@ trace-ust-all.h-timestamp: $(trace-events-files) $(tracetool-y)
 
 trace-ust-all.c: trace-ust-all.c-timestamp
 	@cmp $< $@ >/dev/null 2>&1 || cp $< $@
-trace-ust-all.c-timestamp: $(trace-events-files) $(tracetool-y)
+trace-ust-all.c-timestamp: $(trace-events-files) $(tracetool-y) $(BUILD_DIR)/config-host.mak
 	$(call quiet-command,$(TRACETOOL) \
 		--group=all \
 		--format=ust-events-c \