zsh: fix base_bindir installation

* fixes:
WARNING: zsh-5.3.1-r0 do_package: zsh: NOT adding alternative provide /bin/sh: /bin/zsh does not exist
* it was installing zsh into /usr/bin even when log.do_configure confirms correct path:
installation basename : zsh
binary install path : /bin
* no other files were moved:

$ find 5.3.1-r0.*/image
5.3.1-r0.new/image
5.3.1-r0.new/image/bin
5.3.1-r0.new/image/bin/zsh-5.3.1
5.3.1-r0.new/image/bin/zsh
5.3.1-r0.new/image/usr
5.3.1-r0.old/image
5.3.1-r0.old/image/usr
5.3.1-r0.old/image/usr/bin
5.3.1-r0.old/image/usr/bin/zsh-5.3.1
5.3.1-r0.old/image/usr/bin/zsh

---
 meta-oe/recipes-extended/zsh/zsh_5.3.1.bb | 3 +++
 1 file changed, 3 insertions(+)

index 1f5e390000..96d21a8b34 100644
@@ -30,6 +30,9 @@ EXTRA_OECONF = " \
     zsh_cv_shared_environ=yes \
 "
 
+# Configure respects --bindir from EXTRA_OECONF, but then Src/Makefile will read bindir from environment
+export bindir="${base_bindir}"
+
 EXTRA_OEMAKE = "-e MAKEFLAGS="
 
 ALTERNATIVE_${PN} = "sh"

2.15.1