rust: kconfig: Don't require RUST_IS_AVAILABLE for rustc-option

The final version of this macro does not fail in the absence of an
invokable `$(RUSTC)`, so we don't need to be careful not to invoke it.

Link: https://lore.kernel.org/all/CAGSQo01mQfcU1EiW53be1hcts0c1p-HQAab_HBk6VcVmhq3n2Q@mail.gmail.com/
Signed-off-by: Matthew Maurer <mmaurer@google.com>
Link: https://patch.msgid.link/20250909-docrem-v1-1-dcc69059a5cb@google.com
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: maurer

scripts/Kconfig.include

@@ -73,8 +73,6 @@ rustc-llvm-version := $(shell,$(srctree)/scripts/rustc-llvm-version.sh $(RUSTC))
 
 # $(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_RUST_IS_AVAILABLE is not set.
 # If you are testing for unstable features, consider testing RUSTC_VERSION
 # instead, as features may have different completeness while available.
 rustc-option = $(success,trap "rm -rf .tmp_$$" EXIT; mkdir .tmp_$$; $(RUSTC) $(1) --crate-type=rlib /dev/null --out-dir=.tmp_$$ -o .tmp_$$/tmp.rlib)