"CC=gcc" is almost always incorrect; people often just don't
notice the incorrectness because they are compiling natively.
For an exception, see tzdata.
"guix style" partially made things worse, so I partially ignored it.
* guix/lint.scm (check-compiler-for-target): New linter.
* tests/lint.scm
("compiler-for-target: unconditional CC=gcc is unacceptable")
("compiler-for-target: looks through G-expressions")
("compiler-for-target: (cc-for-target) is acceptable")
("compiler-for-target: CC=gcc is acceptable when target=#false"):
Test it.
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
