gnu: scons: Move to (gnu packages build-tools).

* gnu/packages/python-xyz.scm (scons, scons-python2): Move from here ...
* gnu/packages/build-tools.scm (scons, scons-python2): ... to here.
* gnu/packages/direct-connect.scm, gnu/packages/disk.scm,
gnu/packages/game-development.scm, gnu/packages/gps.scm,
gnu/packages/image.scm, gnu/packages/installers.scm, gnu/packages/web.scm,
gnu/packages/xdisorg.scm: Adjust module imports accordingly.
* guix/build-system/scons.scm (default-scons): Likewise.

gnu/packages/build-tools.scm

@@ -384,6 +384,51 @@ other lower-level build files.")
 scripted definition of a software project and outputs @file{Makefile}s or
 other lower-level build files.")))
 
+(define-public scons
+  (package
+    (name "scons")
+    (version "3.0.4")
+    (source (origin
+             (method git-fetch)
+             (uri (git-reference
+                   (url "https://github.com/SCons/scons")
+                   (commit version)))
+             (file-name (git-file-name name version))
+             (sha256
+              (base32
+               "1xy8jrwz87y589ihcld4hv7wn122sjbz914xn8h50ww77wbhk8hn"))))
+    (build-system python-build-system)
+    (arguments
+     `(#:use-setuptools? #f                ; still relies on distutils
+       #:tests? #f                         ; no 'python setup.py test' command
+       #:phases
+       (modify-phases %standard-phases
+         (add-before 'build 'bootstrap
+           (lambda _
+             (substitute* "src/engine/SCons/compat/__init__.py"
+               (("sys.modules\\[new\\] = imp.load_module\\(old, \\*imp.find_module\\(old\\)\\)")
+                "sys.modules[new] = __import__(old)"))
+             (substitute* "src/engine/SCons/Platform/__init__.py"
+               (("mod = imp.load_module\\(full_name, file, path, desc\\)")
+                "mod = __import__(full_name)"))
+             (invoke "python" "bootstrap.py" "build/scons" "DEVELOPER=guix")
+             (chdir "build/scons")
+             #t)))))
+    (home-page "https://scons.org/")
+    (synopsis "Software construction tool written in Python")
+    (description
+     "SCons is a software construction tool.  Think of SCons as an improved,
+cross-platform substitute for the classic Make utility with integrated
+functionality similar to autoconf/automake and compiler caches such as ccache.
+In short, SCons is an easier, more reliable and faster way to build
+software.")
+    (license license:x11)))
+
+(define-public scons-python2
+  (package
+    (inherit (package-with-python2 scons))
+    (name "scons-python2")))
+
 (define-public tup
   (package
     (name "tup")