Rust: Move 'libformat_parser' build into the GCC build directory

Fixes Rust-GCC#2883.

gcc/rust/ChangeLog:
	* Make-lang.in (LIBFORMAT_PARSER): Point to the GCC build
	directory.
	* ($(LIBFORMAT_PARSER)): Build in the GCC build directory.

gcc/rust/Make-lang.in

@@ -212,7 +212,8 @@ RUST_ALL_OBJS = $(GRS_OBJS) $(RUST_TARGET_OBJS)
 rust_OBJS = $(RUST_ALL_OBJS) rust/rustspec.o
 
 LIBPROC_MACRO_INTERNAL = ../libgrust/libproc_macro_internal/libproc_macro_internal.a
-LIBFORMAT_PARSER = $(srcdir)/../libgrust/libformat_parser/target/debug/liblibformat_parser.a
+LIBFORMAT_PARSER_D = rust/libformat_parser
+LIBFORMAT_PARSER = $(LIBFORMAT_PARSER_D)/debug/liblibformat_parser.a
 
 RUST_LIBDEPS = $(LIBDEPS) $(LIBPROC_MACRO_INTERNAL) $(LIBFORMAT_PARSER)
 
@@ -416,7 +417,13 @@ rust/%.o: rust/lex/%.cc
 
 # TODO: Improve `cargo` invocation with host specific flags, possibly creating a $(CARGO) variable?
 $(LIBFORMAT_PARSER): $(srcdir)/../libgrust/libformat_parser/Cargo.toml $(wildcard $(srcdir)/../libgrust/libformat_parser/src/*.rs)
-	cd $(srcdir)/../libgrust/libformat_parser && cargo build --offline  # FIXME: Not always release, right?
+	cargo \
+	  --config $(srcdir)/../libgrust/libformat_parser/.cargo/config \
+	  build \
+	    --offline \
+	    --target-dir $(LIBFORMAT_PARSER_D) \
+	    --manifest-path $(srcdir)/../libgrust/libformat_parser/Cargo.toml \
+	    # FIXME: Not always '--release', right?
 
 # build all rust/parse files in rust folder, add cross-folder includes
 rust/%.o: rust/parse/%.cc