Makefile: support overriding of CC and CARGO for catching unintended builds.

For CI we want to make sure we don't rebuild.  CC=false doesn't work because
we reply on the output of "$CC -dumpmachine" for the external build directory.

So we would use:

	make CC=devtools/cc-nobuild CARGO=false

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

Makefile

@@ -15,6 +15,7 @@ ECHO := echo
 SUPPRESS_OUTPUT :=
 endif
 
+CARGO := cargo
 DISTRO=$(shell lsb_release -is 2>/dev/null || echo unknown)-$(shell lsb_release -rs 2>/dev/null || echo unknown)
 OS=$(shell uname -s)
 ARCH=$(shell uname -m)

devtools/cc-nobuild

@@ -0,0 +1,9 @@
+#! /bin/sh
+# Version of CC which only supports -dumpmachine (for external/Makefile), and fails otherwise
+set -e
+
+if [ x"$*" = x"-dumpmachine" ]; then
+    CC="$(grep ^CC= config.vars | cut -d= -f2-)"
+    exec ${CC:=cc} "$@"
+fi
+exit 1

plugins/Makefile

@@ -241,7 +241,7 @@ plugins/list_of_builtin_plugins_gen.h: plugins/Makefile Makefile config.vars
 	@$(call VERBOSE,GEN $@,echo "static const char *list_of_builtin_plugins[] = { $(PLUGIN_BASES:%=\"%\",) NULL };" > $@)
 
 $(RUST_TARGET_DIR)/examples/cln-subscribe-wildcard: ${CLN_PLUGIN_SRC} plugins/examples/cln-subscribe-wildcard.rs
-	cargo build ${CARGO_OPTS} --example cln-subscribe-wildcard
+	$(CARGO) build ${CARGO_OPTS} --example cln-subscribe-wildcard
 
 CLN_PLUGIN_EXAMPLES := \
 	$(RUST_TARGET_DIR)/examples/cln-plugin-startup \
@@ -257,17 +257,17 @@ CLN_WSS_PROXY_PLUGIN_SRC = $(shell find plugins/wss-proxy-plugin/src -name "*.rs
 CLN_BIP353_PLUGIN_SRC = $(shell find plugins/bip353-plugin/src -name "*.rs")
 
 $(RUST_TARGET_DIR)/cln-grpc: ${CLN_PLUGIN_SRC} ${CLN_GRPC_PLUGIN_SRC} $(MSGGEN_GENALL) $(MSGGEN_GEN_ALL)
-	cargo build ${CARGO_OPTS} --bin cln-grpc
+	$(CARGO) build ${CARGO_OPTS} --bin cln-grpc
 $(RUST_TARGET_DIR)/clnrest: ${CLN_REST_PLUGIN_SRC}
-	cargo build ${CARGO_OPTS} --bin clnrest
+	$(CARGO) build ${CARGO_OPTS} --bin clnrest
 $(RUST_TARGET_DIR)/cln-lsps-client: ${CLN_LSPS_PLUGIN_SRC}
-	cargo build ${CARGO_OPTS} --bin cln-lsps-client
+	$(CARGO) build ${CARGO_OPTS} --bin cln-lsps-client
 $(RUST_TARGET_DIR)/cln-lsps-service: ${CLN_LSPS_PLUGIN_SRC}
-	cargo build ${CARGO_OPTS} --bin cln-lsps-service
+	$(CARGO) build ${CARGO_OPTS} --bin cln-lsps-service
 $(RUST_TARGET_DIR)/wss-proxy: ${CLN_WSS_PROXY_PLUGIN_SRC}
-	cargo build ${CARGO_OPTS} --bin wss-proxy
+	$(CARGO) build ${CARGO_OPTS} --bin wss-proxy
 $(RUST_TARGET_DIR)/cln-bip353: ${CLN_BIP353_PLUGIN_SRC}
-	cargo build ${CARGO_OPTS} --bin cln-bip353
+	$(CARGO) build ${CARGO_OPTS} --bin cln-bip353
 
 ifneq ($(RUST),0)
 include plugins/rest-plugin/Makefile