Clean up libelf handling.

SConstruct:
    Clean up libelf handling.  Required better handling of
    per-build-root stuff in general (though libelf is the
    only thing in that category currently).
src/SConscript:
    No libelf-specific stuff in here anymore.
src/base/loader/elf_object.cc:
    Just need to include gelf.h... it includes libelf.h.

--HG--
extra : convert_revision : 3d6bdcf8233bda0ac8d08ff777de323df8aa45ae

SConstruct

@@ -105,9 +105,10 @@ def rfind(l, elt, offs = -1):
 # recognize that ALPHA_SE specifies the configuration because it
 # follow 'build' in the bulid path.
 
-# Generate a list of the unique configs that the collected targets
-# reference.
+# Generate a list of the unique build roots and configs that the
+# collected targets reference.
 build_paths = []
+build_roots = []
 for t in abs_targets:
     path_dirs = t.split('/')
     try:
@@ -115,9 +116,12 @@ for t in abs_targets:
     except:
         print "Error: no non-leaf 'build' dir found on target path", t
         Exit(1)
-    config_dir = os.path.join('/',*path_dirs[:build_top+2])
-    if config_dir not in build_paths:
-        build_paths.append(config_dir)
+    build_root = os.path.join('/',*path_dirs[:build_top+1])
+    if build_root not in build_roots:
+        build_roots.append(build_root)
+    build_path = os.path.join('/',*path_dirs[:build_top+2])
+    if build_path not in build_paths:
+        build_paths.append(build_path)
 
 ###################################################
 #
@@ -246,11 +250,6 @@ def no_action(target, source, env):
 
 env.NoAction = Action(no_action, None)
 
-# libelf build is described in its own SConscript file.
-# SConscript-global is the build in build/libelf shared among all
-# configs.
-env.SConscript('src/libelf/SConscript-global', exports = 'env')
-
 ###################################################
 #
 # Define a SCons builder for configuration flag headers.
@@ -292,6 +291,12 @@ config_builder = Builder(emitter = config_emitter, action = config_action)
 
 env.Append(BUILDERS = { 'ConfigFile' : config_builder })
 
+# base help text
+help_text = '''
+Usage: scons [scons options] [build options] [target(s)]
+
+'''
+
 ###################################################
 #
 # Define build environments for selected configurations.
@@ -301,18 +306,24 @@ env.Append(BUILDERS = { 'ConfigFile' : config_builder })
 # rename base env
 base_env = env
 
-help_text = '''
-Usage: scons [scons options] [build options] [target(s)]
-
-'''
+# Spme things (just libelf currently) are shared across all configs in
+# a "build root".  Need to define how to build these just once for
+# each referenced root.
+build_root_env = {}
+for build_root in build_roots:
+    env = base_env.Copy()
+    env.SConscript('ext/libelf/SConscript',
+                   build_dir = os.path.join(build_root, 'libelf'),
+                   exports = 'env')
+    build_root_env[build_root] = env
 
 for build_path in build_paths:
     print "Building in", build_path
     # build_dir is the tail component of build path, and is used to
     # determine the build parameters (e.g., 'ALPHA_SE')
     (build_root, build_dir) = os.path.split(build_path)
-    # Make a copy of the default environment to use for this config.
-    env = base_env.Copy()
+    # Make a copy of the build-root environment to use for this config.
+    env = build_root_env[build_root].Copy()
 
     # Set env options according to the build directory config.
     sticky_opts.files = []