Improved cross-compilation with clang

[asheplyakov]

With this patch I can cross-compile Linux kernel with clang and distcc.
Otherwise both remote compilation and local fallback fail like this:

cat > foo.c <<-EOF
int main(int argc, char **argv) { return 0; }
EOF
env DISTCC_HOSTS=127.0.0.1 distcc clang -c --target=aarch64-linux-gnu- foo.c

error: unknown target triple 'unknown', please use -triple or -arch
distcc[304773] ERROR: compile foo.c on 127.0.0.1 failed
distcc[304773] (dcc_build_somewhere) Warning: remote compilation of 'foo.c' failed, retrying locally
distcc[304773] Warning: failed to distribute foo.c to 127.0.0.1, running locally instead
error: unknown target triple 'unknown', please use -triple or -arch
distcc[304773] ERROR: compile foo.c on localhost failed

Linux' kernel makefiles specify the target arch with --target=foo,
and distcc expects -target foo, hence the problem.

Closes: #416

[shawnl]

the string processing routine is broken

[shawnl]

This is unnecessary. strncmp does this for you.

[asheplyakov]

Let's check it:

char *args[] = { "clang", "-c", "--target=aarch64-linux-gnu", "foo.c", NULL };
int idx = 2;
if (dcc_argv_startswith(args, "--target=") != 1) {
    fprintf(stderr, "wrong answer: args[%d] ('%s') does contain '--target'\n", idx, args[idx]);
    exit(1);
}

Removing for loop from distcc_argv_startswith breaks the test.
Perhaps I'm missing something. Could you elaborate, please? What exactly strncmp is supposed to do?

[shawnl]

oh my bad, I didn't see the double star.