Add basic support for the Blackfin architecture

For uClibc, the name of the Blackfin architecture is 'bfin'. Actually,
the naming of the architecture is quite messy: for toolchain tuples
and uClibc, it's bfin, but for the kernel, it's blackfin. We've
arbitraly choosen to name it "blackfin" in Crosstool-NG.

Add Blackfin-related uClibc patch to fix a build failure related to
fork() being used in unistd/daemon.c.

Yann E. MORIN:
Apply the patch to the kernel/linux build script to use 'linux'
in the noMMU tuples. See:
http://sourceware.org/ml/crossgcc/2010-04/msg00010.html

 diff -durN gcc-4.4.0.orig/boehm-gc/include/gc.h gcc-4.4.0/boehm-gc/include/gc.h

 --- gcc-4.4.0.orig/boehm-gc/include/gc.h	2007-04-23 23:10:09.000000000 +0200

 +++ gcc-4.4.0/boehm-gc/include/gc.h	2009-05-27 21:38:55.000000000 +0200

 @@ -503,7 +503,7 @@

  #if defined(__linux__) || defined(__GLIBC__)

  # include <features.h>

  # if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1 || __GLIBC__ > 2) \

 -     && !defined(__ia64__)

 +     && !defined(__ia64__) && !defined(__UCLIBC__)

  #   ifndef GC_HAVE_BUILTIN_BACKTRACE

  #     define GC_HAVE_BUILTIN_BACKTRACE

  #   endif