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>

package/bash/bash.mk

@@ -28,6 +28,17 @@ BASH_MAKE = $(MAKE1)
 # The static build needs some trickery
 ifeq ($(BR2_PREFER_STATIC_LIB),y)
 BASH_CONF_OPTS += --enable-static-link --without-bash-malloc
+# bash wants to redefine the getenv() function. To check whether this is
+# possible, AC_TRY_RUN is used which is not possible in
+# cross-compilation.
+# On uClibc, redefining getenv is not possible; on glibc and musl it is.
+# Related:
+# http://lists.gnu.org/archive/html/bug-bash/2012-03/msg00052.html
+ifeq ($(BR2_TOOLCHAIN_USES_UCLIBC),y)
+BASH_CONF_ENV += bash_cv_getenv_redef=no
+else
+BASH_CONF_ENV += bash_cv_getenv_redef=yes
+endif
 endif
 
 # Make /bin/sh -> bash (no other shell, better than busybox shells)