runtime(c): Add missing syntax test files

These were missing from commit c2a967a.

closes: #16470

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/c_bool_constant.c

@@ -0,0 +1,11 @@
+// C boolean constants
+
+// Source: https://en.cppreference.com/w/c/language/bool_constant
+
+#include <assert.h>
+
+int main()
+{
+    assert(true == 1 && 0 == false);
+}
+