Move inter-lib dependencies to a project variable and into the build …

…targets.

build.jam

@@ -5,27 +5,30 @@
 
 require-b2 5.2 ;
 
+constant boost_dependencies :
+    /boost/assert//boost_assert
+    /boost/concept_check//boost_concept_check
+    /boost/config//boost_config
+    /boost/container_hash//boost_container_hash
+    /boost/core//boost_core
+    /boost/filesystem//boost_filesystem
+    /boost/integer//boost_integer
+    /boost/iterator//boost_iterator
+    /boost/mp11//boost_mp11
+    /boost/preprocessor//boost_preprocessor
+    /boost/type_traits//boost_type_traits
+    /boost/variant2//boost_variant2 ;
+
 project /boost/gil
     : common-requirements
-        <library>/boost/assert//boost_assert
-        <library>/boost/concept_check//boost_concept_check
-        <library>/boost/config//boost_config
-        <library>/boost/container_hash//boost_container_hash
-        <library>/boost/core//boost_core
-        <library>/boost/filesystem//boost_filesystem
-        <library>/boost/integer//boost_integer
-        <library>/boost/iterator//boost_iterator
-        <library>/boost/mp11//boost_mp11
-        <library>/boost/preprocessor//boost_preprocessor
-        <library>/boost/type_traits//boost_type_traits
-        <library>/boost/variant2//boost_variant2
         <include>include
     ;
 
 explicit
-    [ alias boost_gil ]
+    [ alias boost_gil : : : : <library>$(boost_dependencies) ]
     [ alias all : boost_gil example test ]
     ;
 
 call-if : boost-library gil
     ;
+