debug/cross-gdb: check host dependencies

Cross-gdb depends on expat and python. If either is missing, cross-gdb will
build successfully, but lacking some features.

Especially, if expat is missing, cross-gdb will be unable to parse the target
description, which may lead to runtime malfunctions and the following GDB
warning:
"Can not parse XML target description; XML support was disabled at compile time"

Hence, expat should be considered mandatory.

On the other hand, the features missing without python are not critical, so
python should not be considered mandatory.

This patch does the following:
- At configure time, warn the user if either expat or python is missing.
- In menuconfig, disable the static build options regarding cross-gdb if no
static version of expat is available, and disable cross-gdb if expat is
missing.

Signed-off-by: "Benoît THÉBAUDEAU" <benoit.thebaudeau@advansee.com>
[yann.morin.1998@anciens.enib.fr: add comment for impossible static cross-gdb]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

Signed-off-by: dank@kegel.com

Raising the size of the hash table is a noticable win when linking 

at least one large app.  

There was a patch,

http://sources.redhat.com/ml/binutils/2004-06/msg00165.html

to do this dynamically.  No idea why that didn't make it in.

So this tiny change to raise the default size is just

a stopgap for now.

--- binutils-2.17/bfd/hash.c.old	2006-03-02 23:01:39.000000000 -0800

+++ binutils-2.17/bfd/hash.c	2006-03-02 23:01:58.000000000 -0800

@@ -298,7 +298,7 @@

 */

 /* The default number of entries to use when creating a hash table.  */

-#define DEFAULT_SIZE 4051

+#define DEFAULT_SIZE 32749

 static size_t bfd_default_hash_table_size = DEFAULT_SIZE;

 /* Create a new hash table, given a number of entries.  */