fix(build): Support cross-compilation of Rust binaries (#2178)

Author: alerque

Makefile.am

@@ -179,7 +179,7 @@ CARGO_FEATURE_ARGS += --features variations
 endif
 
 rusile.so: $(rusile_so_SOURCES) $(bin_PROGRAMS)
-	$(CARGO_ENV) $(CARGO) build $(CARGO_VERBOSE) $(RUSILE_FEATURE_ARG) $(CARGO_RELEASE_ARGS) -p rusile
+	$(CARGO_ENV) $(CARGO) build $(CARGO_VERBOSE) --target $(CARGO_TARGET_TRIPLE) $(RUSILE_FEATURE_ARG) $(CARGO_RELEASE_ARGS) -p rusile
 	$(INSTALL) @builddir@/target/@RUST_TARGET_SUBDIR@/lib$@ $@
 
 DEPDIR := .deps

build-aux/que_rust_boilerplate.am

@@ -57,8 +57,8 @@ $(COMPLETIONS_OUT_DIR)/_$(TRANSFORMED_PACKAGE_NAME): $(CARGO_BIN) | $(COMPLETION
 $(_RUST_OUT) $(CARGO_BIN): $(@PACKAGE_VAR@_SOURCES) $(nodist_@PACKAGE_VAR@_SOURCES) $(EXTRA_@PACKAGE_VAR@_SOURCES)
 	set -e
 	export AUTOTOOLS_DEPENDENCIES="$^"
-	$(CARGO_ENV) $(CARGO) build $(CARGO_VERBOSE) $(CARGO_FEATURE_ARGS) $(CARGO_RELEASE_ARGS)
-	$(CARGO_ENV) $(CARGO) build --quiet --message-format=json $(CARGO_FEATURE_ARGS) $(CARGO_RELEASE_ARGS) | \
+	$(CARGO_ENV) $(CARGO) build $(CARGO_VERBOSE) --target $(CARGO_TARGET_TRIPLE) $(CARGO_FEATURE_ARGS) $(CARGO_RELEASE_ARGS)
+	$(CARGO_ENV) $(CARGO) build  --target $(CARGO_TARGET_TRIPLE) --quiet --message-format=json $(CARGO_FEATURE_ARGS) $(CARGO_RELEASE_ARGS) | \
 		$(JQ) -sr 'map(select(.reason == "build-script-executed")) | last | .out_dir' > $(_RUST_OUT)
 
 RUST_DEVELOPER_TARGETS = cargo-test clippy rustfmt

build-aux/que_rust_boilerplate.m4

@@ -22,13 +22,17 @@ AC_DEFUN_ONCE([QUE_RUST_BOILERPLATE], [
                 QUE_PROGVAR([rustfmt])
         ])
 
+        AC_ARG_VAR(CARGO_TARGET_TRIPLE, "Target triple for Rust compilations")
+        if test -z "$CARGO_TARGET_TRIPLE"; then
+                CARGO_TARGET_TRIPLE="$($RUSTC -vV | $SED -n 's/host: //p')"
+        fi
         AC_MSG_CHECKING([whether to build Rust code with debugging information])
         AM_COND_IF([DEBUG_RELEASE], [
                 AC_MSG_RESULT(yes)
-                RUST_TARGET_SUBDIR=debug
+                RUST_TARGET_SUBDIR=$CARGO_TARGET_TRIPLE/debug
         ], [
                 AC_MSG_RESULT(no)
-                RUST_TARGET_SUBDIR=release
+                RUST_TARGET_SUBDIR=$CARGO_TARGET_TRIPLE/release
         ])
         AC_SUBST([RUST_TARGET_SUBDIR])