bash: build with bash_cv_getcwd_malloc=yes on musl too

bash: build with bash_cv_getcwd_malloc=yes on musl too

This fixes bash using its own broken getcwd() during cross compiling
The configure script assumes that your getcwd() function is broken.
Which then makes bash use it's own getcwd() implementation, which
doesn't work if the path to the current directory
contains bind mounts in its paths. This shows up as:

Fixes errors on musl images like
shell-init: error retrieving current directory: getcwd: cannot access parent directories: Bad file descriptor

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>