diff -up src/module_list.py.orig src/module_list.py
--- src/module_list.py.orig	2018-08-29 08:34:50.846439644 -0600
+++ src/module_list.py	2018-08-29 08:35:19.927079956 -0600
@@ -3,7 +3,7 @@ from glob import glob
 from distutils.extension import Extension
 from sage.env import SAGE_LOCAL
 
-SAGE_INC = os.path.join(SAGE_LOCAL, 'include')
+SAGE_INC = '/usr/include'
 
 #########################################################
 ### pkg-config setup
diff -up src/sage/misc/cython.py.orig src/sage/misc/cython.py
--- src/sage/misc/cython.py.orig	2018-08-03 05:10:09.000000000 -0600
+++ src/sage/misc/cython.py	2018-08-29 08:35:19.954079622 -0600
@@ -601,7 +601,7 @@ def cython(filename, verbose=0, compile_
     ext = Extension(name,
                     sources=[pyxfile] + extra_sources,
                     libraries=libs,
-                    library_dirs=[os.path.join(SAGE_LOCAL, "lib")] + libdirs,
+                    library_dirs=[os.path.realpath(os.path.join(SAGE_LOCAL, "lib"))] + libdirs,
                     extra_compile_args=extra_args,
                     language=language)
 
diff -up src/setup.py.orig src/setup.py
--- src/setup.py.orig	2018-08-03 05:10:09.000000000 -0600
+++ src/setup.py	2018-08-29 08:35:19.955079610 -0600
@@ -370,9 +370,8 @@ class sage_build_cython(Command):
             # Debugging
             gdb_debug=self.debug,
             output_dir=os.path.join(self.build_lib, "sage"),
-            # Disable Cython caching, which is currently too broken to
-            # use reliably: http://trac.sagemath.org/ticket/17851
-            cache=False,
+            # Enable Cython caching (the cache is stored in ~/.cycache)
+            cache=True,
             )
 
         # Filter out extensions with skip_build=True
@@ -881,9 +880,6 @@ class sage_install(install):
         install.run(self)
         self.install_kernel_spec()
         log.info('Cleaning up stale installed files....')
-        t = time.time()
-        self.clean_stale_files()
-        log.info('Finished cleaning, time: %.2f seconds.' % (time.time() - t))
 
     def install_kernel_spec(self):
         """
@@ -900,40 +896,6 @@ class sage_install(install):
         # the install_data directory for installing our Jupyter files.
         SageKernelSpec.update(prefix=self.install_data)
 
-    def clean_stale_files(self):
-        """
-        Remove stale installed files.
-
-        This removes files which are built/installed but which do not
-        exist in the Sage sources (typically because some source file
-        has been deleted). Files are removed from the build directory
-        ``build/lib-*`` and from the install directory ``site-packages``.
-        """
-        dist = self.distribution
-        cmd_build_py = self.get_finalized_command("build_py")
-        cmd_build_cython = self.get_finalized_command("build_cython")
-
-        # Determine all Python modules inside all packages
-        py_modules = []
-        for package in dist.packages:
-            package_dir = cmd_build_py.get_package_dir(package)
-            py_modules += cmd_build_py.find_package_modules(package, package_dir)
-        # modules is a list of triples (package, module, module_file).
-        # Construct the complete module name from this.
-        py_modules = ["{0}.{1}".format(*m) for m in py_modules]
-
-        # Clean install directory (usually, purelib and platlib are the same)
-        # and build directory.
-        output_dirs = [self.install_purelib, self.install_platlib, self.build_lib]
-        from sage_setup.clean import clean_install_dir
-        for output_dir in set(output_dirs):
-            log.info('- cleaning {0}'.format(output_dir))
-            clean_install_dir(output_dir,
-                    dist.packages,
-                    py_modules,
-                    dist.ext_modules,
-                    cmd_build_cython.get_cythonized_package_files())
-
 
 #########################################################
 ### Distutils