cargo.bbclass: set up cargo environment in common do_compile

cargo_do_compile runs only if the recipe is built using cargo
as the top level tool. Some recipes hide usage of cargo inside setuptools
(or autoconf) and use do_compile definitions specific to those,
and so the environment isn't properly set up.

This was exposed by latest versions of python3-cryptography.

(From OE-Core rev: a3f566fcbfc02e0a3b3f6a676d6dde88a5b50506)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 9f4ff643a028d7f5670d80861f2ce19ca2d90faa)
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/classes/cargo.bbclass

@@ -49,7 +49,6 @@ oe_cargo_build () {
 
 do_compile[progress] = "outof:\s+(\d+)/(\d+)"
 cargo_do_compile () {
-	oe_cargo_fix_env
 	oe_cargo_build
 }
 

meta/classes/cargo_common.bbclass

@@ -101,6 +101,10 @@ cargo_common_do_configure () {
 	EOF
 }
 
+do_compile:prepend () {
+        oe_cargo_fix_env
+}
+
 oe_cargo_fix_env () {
 	export CC="${RUST_TARGET_CC}"
 	export CXX="${RUST_TARGET_CXX}"