rust: initial merge of most of meta-rust

In the meta-rust repo at commit:
   448047c Upgrade to 1.54.0 (#359)

Make the required directories:
  mkdir ../oe-core/meta/recipes-devtools/rust
  mkdir ../oe-core/meta/recipes-devtools/cargo
  mkdir ../oe-core/meta/recipes-example
and then:
  cp recipes-devtools/rust/* ../oe-core/meta/recipes-devtools/rust
  cp recipes-devtools/cargo/* ../oe-core/meta/recipes-devtools/cargo
  cp lib/crate.py ../oe-core/meta/lib
  cp recipes-example/* ../oe-core/meta/recipes-example
  cp conf/distro/include/rust_* ../oe-core/meta/conf/distro/include/
  cp classes/* ../oe-core/meta/classes/
  cp recipes-core/packagegroups/packagegroup-rust-cross-canadian.bb ../oe-core/meta/recipes-core/packagegroups

(From OE-Core rev: 3ed57578cca93ff1ba4e0bf3f25566e10659a2f9)

Signed-off-by: Randy MacLeod <Randy.MacLeod@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/rust.bbclass

@@ -0,0 +1,45 @@
+inherit rust-common
+
+RUSTC = "rustc"
+
+RUSTC_ARCHFLAGS += "--target=${HOST_SYS} ${RUSTFLAGS}"
+
+def rust_base_dep(d):
+    # Taken from meta/classes/base.bbclass `base_dep_prepend` and modified to
+    # use rust instead of gcc
+    deps = ""
+    if not d.getVar('INHIBIT_DEFAULT_RUST_DEPS'):
+        if (d.getVar('HOST_SYS') != d.getVar('BUILD_SYS')):
+            deps += " virtual/${TARGET_PREFIX}rust ${RUSTLIB_DEP}"
+        else:
+            deps += " rust-native"
+    return deps
+
+DEPENDS:append = " ${@rust_base_dep(d)}"
+
+# BUILD_LDFLAGS
+# 	${STAGING_LIBDIR_NATIVE}
+# 	${STAGING_BASE_LIBDIR_NATIVE}
+# BUILDSDK_LDFLAGS
+# 	${STAGING_LIBDIR}
+# 	#{STAGING_DIR_HOST}
+# TARGET_LDFLAGS ?????
+#RUSTC_BUILD_LDFLAGS = "\
+#	--sysroot ${STAGING_DIR_NATIVE} \
+#	-L${STAGING_LIBDIR_NATIVE}	\
+#	-L${STAGING_BASE_LIBDIR_NATIVE}	\
+#"
+
+# XXX: for some reason bitbake sets BUILD_* & TARGET_* but uses the bare
+# variables for HOST. Alias things to make it easier for us.
+HOST_LDFLAGS  ?= "${LDFLAGS}"
+HOST_CFLAGS   ?= "${CFLAGS}"
+HOST_CXXFLAGS ?= "${CXXFLAGS}"
+HOST_CPPFLAGS ?= "${CPPFLAGS}"
+
+rustlib_suffix="${TUNE_ARCH}${TARGET_VENDOR}-${TARGET_OS}/rustlib/${HOST_SYS}/lib"
+# Native sysroot standard library path
+rustlib_src="${prefix}/lib/${rustlib_suffix}"
+# Host sysroot standard library path
+rustlib="${libdir}/${rustlib_suffix}"
+rustlib:class-native="${libdir}/rustlib/${BUILD_SYS}/lib"