cast: make sure suncc sees a constant.

cast_const() et. al. are supposed to be a constant expression, so you can do things like:
	static char *p = cast_const(char *, (const char *)"hello");

Unfortunately, a cast to intptr_t and arithmetic makes suncc reject it as
a constant expression.  We need the cast, because (1) the expression could be
a void *, so we can't just add to it, and (2) gcc complains with -Wcast-qual
without it.

So instead of adding BUILD_BUG_OR_ZERO, we use a ? :, which keeps everyone happy.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
(Imported from CCAN commit 74859ab18b10aaf990848e49d7789ff5c6cf96c6)

Autobuild-User: Rusty Russell <rusty@rustcorp.com.au>
Autobuild-Date: Thu Mar 29 08:18:57 CEST 2012 on sn-devel-104

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/ccan/cast/test/compile_ok-static.c b/lib/ccan/cast/test/compile_ok-static.c
new file mode 100644
index 0000000000..98b667e834
--- /dev/null
+++ b/lib/ccan/cast/test/compile_ok-static.c
@@ -0,0 +1,10 @@
+/* OpenIndiana's CC (aka suncc) has issues with constants: make sure
+ * we are one! */
+#include <ccan/cast/cast.h>
+
+static char *p = cast_const(char *, (const char *)"hello");
+
+int main(int argc, char *argv[])
+{
+	return p[0] == argv[0][0];
+}