The "/usr/include/assert.h" from FreeBSD causes C++ compilation to fail when an assertion is done and the compiler is non-GCC _and_ does not define "__GNUC__" _and_ "NDEBUG" is not defined.  It`s a simple and quick fix.

Fix: *** /usr/include/assert.h       2009-10-02 01:24:01.000000000 -0500
--- /tmp/assert.h___new 2011-08-28 21:39:12.000000000 -0500
***************
*** 66,72 ****
  __END_DECLS

  #define assert(e)  \
!     ((void) ((e) ? 0 : __assert (#e, __FILE__, __LINE__)))
  #define __assert(e, file, line) \
      ((void)printf ("%s:%u: failed assertion `%s'\n", file, line, e), abort())

--- 66,72 ----
  __END_DECLS

  #define assert(e)  \
!     ((void) ((e) ? ((void)0) : __assert (#e, __FILE__, __LINE__)))
  #define __assert(e, file, line) \
      ((void)printf ("%s:%u: failed assertion `%s'\n", file, line, e), abort())
q

Patch attached with submission follows:
How-To-Repeat: compile this:

#include <cassert>
int main() {
  assert(1);
}

like this [assuming Clang is installed and is on the PATH]:

clang++ -U__GNUC__ test.cpp

 and one of the errors you get is this:

test.cpp:3:3: error: right operand to ? is void, but left operand is of type 'int'
  assert(1);
  ^~~~~~~~~
In file included from test.cpp:1:
In file included from /usr/include/c++/4.2.1/cassert:48:
/usr/include/assert.h:69:18: note: instantiated from:
    ((void) ((e) ? 0 : __assert (#e, __FILE__, __LINE__)))
                 ^ ~