(cvs head) CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK breaks

[strauman at slac.stanford.edu (Till Straumann)]

Recently a configuration option (CONFIGURE_MALLOC_BSP_SUPPORTS_SBRK)
had been added. Unfortunately, on BSPs (e.g., the ones using 
powerpc/shared/)
which rely on sbrk() to provide the first chunk of memory using sbrk is not
really optional.

IMHO, confdefs.h is the wrong place for conditionally including sbrk 
support.

Instead, I'd propose to make this (yet another) variable to be 
initialized by the
BSP (could be statically initialized to NULL and overridden by BSP's 
bsp_start)

-- Till