kernel/Cargo.toml: Add default-test cargo feature

Add the default-test cargo feature to control what features we want to enable in
the tests. The vtpm/mstpm/wrappers.rs, for example, can't run in the test
environment because its malloc() etc functions conflict with the libc standard
libraries.

This was working before, but now it is not working as expected.
"cargo test --workspace" is not honoring --no-default-features for workspace members.
rust-lang/cargo#7160

Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>

Makefile

@@ -1,6 +1,9 @@
 FEATURES ?= "default"
 SVSM_ARGS = --features ${FEATURES}
 
+FEATURES_TEST ?= "default-test"
+CARGO_ARGS_TEST = --no-default-features --features ${FEATURES_TEST}
+
 ifdef RELEASE
 TARGET_PATH=release
 CARGO_ARGS += --release
@@ -14,8 +17,10 @@ endif
 
 ifeq ($(V), 1)
 CARGO_ARGS += -v
+CARGO_ARGS_TEST += -v
 else ifeq ($(V), 2)
 CARGO_ARGS += -vv
+CARGO_ARGS_TEST += -vv
 endif
 
 STAGE2_ELF = "target/x86_64-unknown-none/${TARGET_PATH}/stage2"
@@ -62,7 +67,7 @@ bin/coconut-test-qemu.igvm: $(IGVMBUILDER) bin/test-kernel.elf bin/stage2.bin
 	$(IGVMBUILDER) --sort --output $@ --stage2 bin/stage2.bin --kernel bin/test-kernel.elf qemu
 
 test:
-	cargo test --workspace --target=x86_64-unknown-linux-gnu
+	cargo test --workspace ${CARGO_ARGS_TEST} --target=x86_64-unknown-linux-gnu
 
 test-in-svsm: utils/cbit bin/coconut-test-qemu.igvm
 	./scripts/test-in-svsm.sh

kernel/Cargo.toml

@@ -36,6 +36,7 @@ test.workspace = true
 
 [features]
 default = ["mstpm"]
+default-test = []
 enable-gdb = ["dep:gdbstub", "dep:gdbstub_arch"]
 fuzzing-hooks = []
 mstpm = ["dep:libmstpm"]