build: Honor the user's $GUILE_LOAD_COMPILED_PATH.

Until now '.go' files of all the dependencies would not be found,
and thus building would take a long time.

* env.in: Append to the user's $GUILE_LOAD_COMPILED_PATH.  Don't set
GUILE_WARN_DEPRECATED.

env.in

 #!/bin/sh
 
-GUILE_LOAD_PATH=@abs_top_srcdir@:$GUILE_LOAD_PATH
+GUILE_LOAD_PATH="@abs_top_srcdir@:$GUILE_LOAD_PATH"
 if test "@abs_top_srcdir@" != "@abs_top_builddir@"; then
-    GUILE_LOAD_PATH=@abs_top_builddir@:$GUILE_LOAD_PATH
+    GUILE_LOAD_PATH="@abs_top_builddir@:$GUILE_LOAD_PATH"
 fi
-GUILE_LOAD_COMPILED_PATH=@abs_top_builddir@:$GUILE_LOAD_PATH
-PATH=@abs_top_builddir@/bin:$PATH
+GUILE_LOAD_COMPILED_PATH="@abs_top_builddir@:$GUILE_LOAD_COMPILED_PATH"
+PATH="@abs_top_builddir@/bin:$PATH"
 
-GUILE_WARN_DEPRECATED="no"
-
-export GUILE_WARN_DEPRECATED
 export GUILE_LOAD_PATH
 export GUILE_LOAD_COMPILED_PATH
 export PATH