go-cross: don't use host /var/tmp for temporary build artifacts

The default behavior for go-cross build is to use the path specified
in TMPDIR for some temporary build artifacts and if no TMPDIR is set
in the environment to fallback to use /var/tmp. This causes a build
failure on hosts that do not have a /var/tmp or that have restrictive
permissions on /var/tmp. The failure is seen as:

  go tool dist: mkdtemp(/var/tmp/go-cbuild-yhmNbi): No such file or directory

By setting TMPDIR and ensuring we create this
directory we can avoid the associated issue with using the default.

Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>

recipes-devtools/go-cross/go-cross.inc

@@ -20,6 +20,10 @@ do_compile() {
     export GOBIN="${B}/bin"    
     rm -rf ${GOBIN} ${B}/pkg
     mkdir ${GOBIN}
+
+    export TMPDIR=${WORKDIR}/build-tmp
+    mkdir ${WORKDIR}/build-tmp
+
     cd src
     ./make.bash --host-only
 }