Ensure CC/CXX are passed into bdlib.

This fixes the build on systems with gcc6 and clang since wraith wants
gcc6 and bdlib wants clang.  Now bdlib will use whatever wraith
wanted.

build/autotools/configure.ac

@@ -278,6 +278,7 @@ if test -d .git; then
 fi
 ]
 
+export CC CXX
 if [[ -f lib/bdlib/configure ]]; then
   AC_CONFIG_SUBDIRS([lib/bdlib])
 fi

configure

@@ -8577,6 +8577,7 @@ if test -d .git; then
 fi
 
 
+export CC CXX
 if [ -f lib/bdlib/configure ]; then