As a side effect, this fixes the T4113 test on OS X

Fixes the test on OS X

-fvia-c is now a no-op

The underlying problem in ticket #5003 is not in ghc, but rather
that the test condition runs off the end of the C stack on 64 bit
processors.

Test 4038 does a recursive call of a simple external function.
Each invocation of the function allocates a bit over 16 kB of C stack
on a 64 bit processor (half as much on a 32 bit processor).  The
typical C stack on a unix system is 8 MB, so after no more than
about 500 nested calls the stack pointer will move past the end
of the allocated stack and cause a segfault.

The fix is to not call the function as many times.  I've made the
number of calls a constant and have added a note explaining its
value.

With this patch test 4038 passes consistently on OS X 64 bit.