oe-buildenv-internal: Fix BITBAKEDIR changes to work with existing autobuilder scritpts

The BITBAKEDIR change does not work well when the script is sourced from another script
since $2 may be unrelated. This change adds the logic onto the BDIR conditional and
which more external scripts would set, hence avoiding the problem.

(From OE-Core rev: ec8fbe0d1870285a4a972ddcfe83aa63d720cb80)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/oe-buildenv-internal

@@ -46,6 +46,9 @@ if [ "x$BDIR" = "x" ]; then
             return 1
         fi
     fi
+    if [ "x$2" != "x" ]; then
+        BITBAKEDIR="$2"
+    fi
 fi
 if expr "$BDIR" : '/.*' > /dev/null ; then
     BUILDDIR="$BDIR"
@@ -54,10 +57,8 @@ else
 fi
 unset BDIR
 
-if [ "x$2" = "x" ]; then
+if [ "x$BITBAKEDIR" = "x" ]; then
     BITBAKEDIR="$OEROOT/bitbake$BBEXTRA/"
-else
-    BITBAKEDIR="$2"
 fi
 
 BITBAKEDIR=`readlink -f "$BITBAKEDIR"`