recipes: Switch away from S = WORKDIR

Where recipes use S = ${WORKDIR}, change them to set UNPACKDIR to
a subdir of WORKDIR and make S point at this instead.

I've chosen not to force S into any standard UNPACKDIR we may pick in
future just so the S = UNPACKDIR case is clearly visible by the
directory naming under WORKDIR as that should aid usability.

(From OE-Core rev: d9328e3b0b062f0621de3d114584b44f384a1c02)

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

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

@@ -12,7 +12,8 @@ DEPENDS += "virtual/${SDK_PREFIX}gcc virtual/nativesdk-libc virtual/nativesdk-${
 
 SRC_URI += "file://target-rust-ccld.c"
 LIC_FILES_CHKSUM = "file://target-rust-ccld.c;md5=af4e0e29f81a34cffe05aa07c89e93e9;endline=7"
-S = "${WORKDIR}"
+S = "${WORKDIR}/sources"
+UNPACKDIR = "${S}"
 
 # Need to use our SDK's sh here, see #14878
 create_sdk_wrapper () {