gnu: Define `native-search-paths' for Automake, Guile, and Python.

* gnu/packages/autotools.scm (automake)[native-search-paths]: New field.
* gnu/packages/guile.scm (guile-1.8)[native-search-paths]: New field.
  (guile-2.0)[native-search-paths]: New field.
* gnu/packages/python.scm (python)[native-search-paths]: New field.

gnu/packages/autotools.scm

@@ -164,6 +164,11 @@ exec ~a --no-auto-compile \"$0\" \"$@\"
                      (setenv "SHELL" sh)
                      (setenv "CONFIG_SHELL" sh)))
                  %standard-phases)))
+    (native-search-paths
+     (list (search-path-specification
+            (variable "ACLOCAL_PATH")
+            (directories '("share/aclocal")))))
+
     (home-page "http://www.gnu.org/software/automake/")
     (synopsis
      "GNU Automake, a GNU standard-compliant makefile generator")

gnu/packages/guile.scm

@@ -88,6 +88,11 @@
    ;; When cross-compiling, a native version of Guile itself is needed.
    (self-native-input? #t)
 
+   (native-search-paths
+    (list (search-path-specification
+           (variable "GUILE_LOAD_PATH")
+           (directories '("share/guile/site")))))
+
    (synopsis "GNU Guile 1.8, an embeddable Scheme interpreter")
    (description
 "GNU Guile 1.8 is an interpreter for the Scheme programming language,
@@ -137,6 +142,14 @@ extensible.  It supports many SRFIs.")
                        (string-append bash "/bin/bash")))))
                 %standard-phases)))
 
+   (native-search-paths
+    (list (search-path-specification
+           (variable "GUILE_LOAD_PATH")
+           (directories '("share/guile/site/2.0")))
+          (search-path-specification
+           (variable "GUILE_LOAD_COMPILED_PATH")
+           (directories '("share/guile/site/2.0")))))
+
    (synopsis "GNU Guile 2.0, an embeddable Scheme implementation")
    (description
 "GNU Guile is an implementation of the Scheme programming language, with

gnu/packages/python.scm

@@ -43,6 +43,10 @@
      `(("zlib" ,zlib)
        ("openssl" ,openssl)
        ("bzip2" ,bzip2)))
+    (native-search-paths
+     (list (search-path-specification
+            (variable "PYTHONPATH")
+            (directories '("lib/python2.7/site-packages")))))
     (home-page "http://python.org")
     (synopsis
      "Python, a high-level dynamically-typed programming language")