bash: fix linking for static builds with uClibc toolchains

bash fails to link for static builds with uClibc toolchains due to
getenv redefinitions. This is caused because bash is unable to check if
getenv is already defined when cross-compiling, so it defaults to 'yes':

configure:14438: WARNING: cannot check getenv redefinition if cross
compiling -- defaulting to yes

We can avoid this redefinition by passing bash_cv_getenv_redef=no to the
configure script.

Related:
	http://lists.gnu.org/archive/html/bug-bash/2012-03/msg00052.html

Fixes:
	http://autobuild.buildroot.net/results/a20/a2007e6dbcfe53e7cd837ae642869ee26376826a/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>