rust-target-config: Create new class to contain target json config generation

Currently most of the rust recipes use this code but it is all piecemeal.
Turn the code into a class where things can start to be rationalised. Ultimately
some of the data and python code should be moved to a python library but one step
at a time.

No functionality changes.

(From OE-Core rev: 3795285cbf362e13b8151bfdbe1bce999ac28641)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/rust-target-config.bbclass

@@ -1,4 +1,3 @@
-
 # Right now this is focused on arm-specific tune features.
 # We get away with this for now as one can only use x86-64 as the build host
 # (not arm).

meta/recipes-devtools/cargo/cargo-cross-canadian.inc

@@ -5,7 +5,7 @@ RUST_ALTERNATE_EXE_PATH = "${STAGING_LIBDIR_NATIVE}/llvm-rust/bin/llvm-config"
 HOST_SYS = "${HOST_ARCH}-unknown-linux-gnu"
 CARGO_RUST_TARGET_CCLD = "${RUST_BUILD_CCLD}"
 
-require recipes-devtools/rust/rust-common.inc
+inherit rust-target-config
 require cargo.inc
 
 CARGO = "${WORKDIR}/${CARGO_SNAPSHOT}/bin/cargo"

meta/recipes-devtools/rust/rust.inc

@@ -39,7 +39,7 @@ setup_cargo_environment () {
     printf "linker = '%s'\n" "${RUST_BUILD_CCLD}" >> ${CARGO_HOME}/config
 }
 
-include rust-common.inc
+inherit rust-target-config
 
 do_rust_setup_snapshot () {
     for installer in "${WORKDIR}/rust-snapshot-components/"*"/install.sh"; do