rust: Define probing macros for rustc

Creates flag probe macro variants for `rustc`. These are helpful
because:

1. `rustc` support will soon be a minimum rather than a pinned version.
2. We already support multiple LLVMs linked into `rustc`, and these are
   needed to probe what LLVM parameters `rustc` will accept.

Signed-off-by: Matthew Maurer <[email protected]>

Author: maurer

scripts/Kconfig.include

@@ -63,3 +63,8 @@ ld-version := $(shell,set -- $(ld-info) && echo $2)
 cc-option-bit = $(if-success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null,$(1))
 m32-flag := $(cc-option-bit,-m32)
 m64-flag := $(cc-option-bit,-m64)
+
+# $(rustc-option,<flag>)
+# Return y if the Rust compiler supports <flag>, n otherwise
+# Calls to this should be guarded so that they are not evaluated if CONFIG_HAVE_RUST is not set.
+rustc-option = $(success,trap "rm -rf .tmp_$$" EXIT; mkdir .tmp_$$; $(RUSTC) $(1) --crate-type=rlib /dev/null -o .tmp_$$/tmp.rlib)

scripts/Makefile.compiler

@@ -72,3 +72,18 @@ clang-min-version = $(call test-ge, $(CONFIG_CLANG_VERSION), $1)
 # ld-option
 # Usage: KBUILD_LDFLAGS += $(call ld-option, -X, -Y)
 ld-option = $(call try-run, $(LD) $(KBUILD_LDFLAGS) $(1) -v,$(1),$(2),$(3))
+
+# __rustc-option
+# Usage: MY_RUSTFLAGS += $(call __rustc-option,$(RUSTC),$(MY_RUSTFLAGS),-Cinstrument-coverage,-Zinstrument-coverage)
+__rustc-option = $(call try-run,\
+	$(1) $(2) $(3) --crate-type=rlib /dev/null -o "$$TMP",$(3),$(4))
+
+# rustc-option
+# Usage: rustflags-y += $(call rustc-option,-Cinstrument-coverage,-Zinstrument-coverage)
+rustc-option = $(call __rustc-option, $(RUSTC),\
+	$(KBUILD_RUSTFLAGS),$(1),$(2))
+
+# rustc-option-yn
+# Usage: flag := $(call rustc-option-yn,-Cinstrument-coverage)
+rustc-option-yn = $(call try-run,\
+	$(RUSTC) $(KBUILD_RUSTFLAGS) $(1) --crate-type=rlib /dev/null -o "$$TMP",y,n)