do not error out on incompatible function pointer casts

In many cases, the callback function pointers in PyMethodDef definitions are
cast to PyCFunction type where as their actual signature matches that of
PyCFunctionWithKeywords type. This issue exists throughout in python 2.7
codebase in general. On newer compilers, this produces a compile time failure
like the following:

build/grub/grub-core/contrib/python/bitsmodule.c:558:16: error: cast between incompatible function types from 'PyObject * (*)(PyObject *, PyObject *, PyObject *)' {aka 'struct _object * (*)(struct _object *, struct _object *, struct _object *)'} to 'PyObject * (*)(PyObject *, PyObject *)' {aka 'struct _object * (*)(struct _object *, struct _object *)'} [-Werror=cast-function-type]
  558 |     {"get_xy", (PyCFunction)bits_get_xy, METH_KEYWORDS, "get_xy(term) -> (cursor_x, cursor_y)"},

Pass -Wno-cast-function-type in compiler cflags in order to suppress this
failure.

Signed-off-by: Ani Sinha <[email protected]>

Author: ani-sinha

configure.ac

@@ -1121,6 +1121,9 @@ yes)
       BASECFLAGS="$BASECFLAGS -fno-strict-aliasing"
     fi
 
+    # disable cast function type warning for newer compilers
+    BASECFLAGS="$BASECFLAGS -Wno-cast-function-type"
+
     # if using gcc on alpha, use -mieee to get (near) full IEEE 754
     # support.  Without this, treatment of subnormals doesn't follow
     # the standard.