Test fallthrough in OSSH_CHECK_CFLAG_COMPILE.

clang 10's -Wimplicit-fallthrough does not understand /* FALLTHROUGH */
comments and we don't use the __attribute__((fallthrough)) that it's
looking for.  This has the effect of turning off -Wimplicit-fallthrough
where it does not currently help (particularly with -Werror).  ok djm@

1 files changed, 10 insertions, 0 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 25ecc49a2..0193c3dcc 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -21,6 +21,16 @@ int main(int argc, char **argv) {
         double m = l / 0.5;
         long long int n = argc * 12345LL, o = 12345LL * (long long int)argc;
         printf("%d %d %d %f %f %lld %lld\n", i, j, k, l, m, n, o);
+        /*
+         * Test fallthrough behaviour.  clang 10's -Wimplicit-fallthrough does
+         * not understand comments and we don't use the "fallthrough" attribute
+         * that it's looking for.
+         */
+        switch(i){
+        case 0: j += i;
+                /* FALLTHROUGH */
+        default: j += k;
+        }
         exit(0);
 }
         ]])],